Hot soak start rough idle

Has anyone solved the rough idle on start after sitting 10-20 minutes hot? I have new plugs, wires, coils. Van runs great all other times. If I give it gas, the engine is still rough even at 1500-2000 rpm, so I doubt a little vacuum leak that cause rough idle could corrupt engine run at that speed. With key on, before starting, TPS is fine, air & coolant temp seem reasonable. AFter starting, the air flow reads 1.12lb/min, which seems high given the idle is about 6-700rpm. After several seconds it smooths out. At smooth idle, air flow is .88lb/min. A normal restart the engine rpm jumps to 1200 (air flow 1.12lb/min) then settles to 800 idle and .88lb/min. I guess it could be IAC, but I cleaned it all up and no change. No pending codes.
I just watched it and it almost seemed like the engine smoothed out as air temp dopped below 130, it starts out at 135-140. its a 80deg day, seems reasonable. 180,000 miles on van. I cleaned EGR ports just 20,000 miles ago.

I pulled air temp sensor out and heated it by hand, started fine with 135deg air temp. maybe it's fuel pressure related, maybe the MAF has some temp issues. I went ahead and sprayed the MAF with brake cleaner to see if that helps.

I have had this problem....intermittently for years.
I have no idea of what causes it.
I used to think that it was related to my slightly leaking lower intake manifold gaskets.....but they have been replaced....no more coolant usage.......and it still happens....

I have replaced the Constant Control Relay Module (CCRM) with the updated version......no change.....newer windstars have the fuel pump relay in the power distribution box....and that relay is known to cause issues.

The good news is.....on my vehicle.....it has not developed into anything worse in well over 100K miles and many years.

I had a GM car that did that and it turned out to be a bad fuel pressure regulator. As the engine was turned off the fuel was still bleeding thru from the fuel pump pressure buildup.

Best way to test would be to have someone start the van while you check the exhaust tail pipe for signs of raw fuel, either smell of raw fuel or black smoke pumping out as the engine clears up.

Could also be an injector stuck open or acting up!

My 96 did this when I had bad lower intake gaskets, coolant was geting into the intake port. I also thought my starter was going bad once when the engine cranked about 1/2 a turn and stoped, on the next try it sounded lke it was bound up then started cranking. I think it was hydrolocked.

Has not done it since I replaced the gaskets.

Wonder if it has anything to do with the cold knock that recently devolped??

I will have to repeat this to be sure, after stopping the van hot, I put on fuel pressure guage, I keep fitting a gauage loose so all fuel pressure would bleed off and keep zero pressure in line while I waited 15min. I then
tightened up guage, key one pressure went to 20. Van started fine, quick jump to 1500 rpm and settled down to normal rpm, 30psi pressure. it still seemed like the idle was a little rough for several seconds, but not bad. I shut off engine, waited 15 min, fuel pressure held at 30 the whole time, restarted fine. So did I prove anything, or just get one of those times it wasn't going to act up? Could an injector be leaking only when its hot?

After this symptom first started, I ran 50/50 mix of sea foam and gas into gas line with fuel pump off using pressure canister. I would have thought that would cleaned up the injectors.
Note, a bad start after hot soak would not get me the jump to 1500 rpm, it would hit maybe 1000, and settle to 600 rpm rough idle for 20-30 seconds.
I will keep fighting this, but if I suspect a hot only leaky injector, how will I identify which one, have to think about that.

My problem has been intermittent enough that there is no way that I can troubleshoot it.

I replaced the fuel pressure regulator, EGR valve....and a whole bunch of other stuff, while trying to troublshoot a slight miss, which turned out to be a dirty fuel injector.....once the slight miss was bad enough to finally light up the CEL....I had that one nailed in super quick order.....

I also have driven with the ScanGauge connected to the OBDII port and verified the throttle position sensor, intake air temperature sensor, Coolant temperature sensor......etc.
I had it before the lower intake manifold gasket job.....thought that that must have been it...has not used any coolant since that repair........but it has happened a few times since then.

It has done it with 3 different CCRM units (the older windstars have those....newer ones don't).....which were replaced for radiator fan issue, and A/C compressor issue.

So....in my case.....until it turns into something more serious.....I am not going to worry about it....

I have the exact same problem. I have spent many hours searching the internet for answers. Occasionally I will come across a post describing the same problem but never a solution. Mine does it really bad and is consistant with every hot start after it sets for about 10 - 30 minutes or soo. The only thing I have been able to do to make it better is to unhook the vacuum line to the fuel pressure regulator. This raises the fuel pressure about 8-10 pounds and helps the idle smoot out immidiately. This indicates to me that I have a lean condition. It acts like the fuel is boiling in the injectors or fuel lines when it is hot and clears itself out after the hot fuel is moved through the system. But I'm just guessing at this point. I have worked on this for days with no improvement.

If the fuel is more or less vapor locking, then I think cycling the key on and off a couple of time before hot soak starting should help, I think the fuel pressure regulator will bleed off excess gas each cycle and you should have cool gas when starting.
In my case, the rough idle last so long, and I see good fuel pressure, I think there is more than enough time for cool gas to be getting to the fuel rail. I just don't think the rough idle could last as long as it does if all it needed was cool gas.
As the weather is warming, I seem to be at 90% problem rate, I need to get this fixed.
I am leaning towards a bad injector flooding engine. If only I saw black smoke, the exhaust does smell bad. I will most likely pull them and send off for testing and ultrasonic cleaning. At about $120, it's not much more $ than throwing parts at it.

I understand what you are saying but if it was a leaking injector, raising the fuel pressure would only make it worse for me and not better. Also, I live in indiana and mine does it even if it is 10 degree's outside so I tend to think it has to do with the heat under the hood. What troubles me is that this only occures for about a minute and then clears up. Something has to be changing. A dirty/leaking injector, air/vacuum leak shouldn't change so the lean condition should always exist but it my case it doesn't. The engine runs great - no pinging, not sluggish, etc... It's just :banghead:

the symptoms are so confusing,

it really bothers me the MAF sensor is reporting 1.2 lb/min airflow when the rpm is struggling at 500rpm, and if I give it throttle, the reading goes up, but is too high. if the engine is just a air pump, the volume of air for a given rpm should be pretty constant.
at 500 rpm it should be reading 0.5lb/min.

I wish my scan tool showed injector pulse width.

Also, I tried to monitor both O2 sensors, both seem to read very lean, maybe normal until they warm up. one O2 sensor starts jumping healthy, and the roughness improves, the other O2 sensor stays lean for several more seconds, and the last bit of roughness doesn't go away till it starts bouncing. On a good hot restart, both O2 sensors seemed to come alive showing rich, together, until close loop mode is started.

I repeated your experiment with pulling vacume line of FPR, within the first few seconds of really bad idle it didn't help, later on it did.

After hot soak, I toggled the key several times till the fuel rail was no longer hot, still started bad.

Plugging the vacume line to PCV and Evaporative canister didn't help.

I just cannot think of another explination why removing pressure in fuel rail during hot soak fixes the problem other than injector issue. But that doesn't explain all the symptoms.

this post leans to my theory

http://www.automotiveforums.com/vbulletin/showthread.php?t=516738

finally got the wife to give up the van, pulled out fuel rail, key on to run fuel pump, no sign of any leaks. But I will go ahead and send them off for cleaning and flow testing. With 190,000 miles on them, might as well. Maybe I will get lucky and after cleaning pick up some MPG.

the injectors came back from getting cleaned, the good news, at 190,000 miles they had good spray pattern and volume, cleaning did not improve anything. the bad news, van still has rough idle after hot soak. will have to give up on this for now.

a new IAC appears to have solved this issue, need a few more hot days to be sure.

Had basically the same problem with a 1999 4.0L Jeep Grand Cherokee. Jeep put out a Service Bulletin (No. 18-031-03) with the condition (as consistent with stop-and-go driving -aggrevated by higher ethanol fuels), a MIL may occur due to Cylinder #3 misfire, wherein heat from the exhaust manifold following engine shutdown migrates to the area around the injector #3 and causes fuel vapor to form within the injector. Recommend installing an injector sleeve around injector #3 with the slit of the sleeve upward facing and installing another sleeve on the downward facing side of the injector.

One possible explanation I see is that maybe the hot weather elevated the fuel pressure in the fuel tank, causing increased fuel pressure as the fuel pump ran at normal speed to start (i.e. extra fuel pump "head"), and thus an engine rich condition until the engine could reduce the injector pulse width to compensate and bring the engine back to a good stoichiometric ratio, which could take a few seconds at startup.

I was just reading through a service manual yesterday which mentioned that fuel tank pressure is often elevated after a fillup, hot weather, or extended driving. If your EVAP system isn't in perfect working order, I could see how you could get enough pressure buildup to mess with the fuel system. I seem to have that problem myself after a fillup sometimes. It seems like a way to check that would be to start the car with the fuel cap off to see if that helps. Should have zero pressure in the fuel tank then.

I've seen this problem. When it occurs on my vehicle, after sitting for 10-20 minutes (about long enough to go into a store and return), you could hear a gurgling noise from under the floor, apparently the fuel tank. It's not loud enough to hear it if the seat belt alarm was ringing or the radio was turned on. Since the fuel pump only runs for a couple seconds when the ignition key is turned on, the gurgling noise dies off after the fuel pump stops running. I presume this noise is not air, but gasoline vapors trapped in the fuel lines, as suggested in the previous post.

If you turn the key off and on again, the gurggling can be heard again. This can be repeated until the gurggling noise is not heard, and only the pump motor can be heard. If the car is started after the vapor has been cleared from the fuel lines, it runs normally. If the car is started before all the vapor is cleared, it misfires for a few minutes then runs fine, apparently until the fuel pump runs enough to clear the vapors.

I also saw another cause of "hot start misfire". In this case, the misfire would start if the vehicle was hot started even after being shut down for only a minute or two. Sometimes it would not stop misfiring, but most of the time it would clear up after driving a few hundred yards. It believe the cause was clogged EGR ports under the upper intake manifold. The misfires stopped and the CEL self-cleared a few drive cycles after I cleaned them.

PS. I did not notice the date of the original question on this thread. Hopefully the additional information will be helpful to someone.

Well the problem came back a few months after the new IAC, it really was fixed. I traded in IAC for a new IAC, didn't help. then the weather got cool and symptoms weren't too bad, since the heat has come back I tried replacing the TPS, scan tool showed absolutely no issues with TPS, but I was getting desperate, and part was cheap enough. So FAR is has fixed my problem. Time will well. FYI my TPS screws were so frozen, had to cut slot in heads and use large flat blade to get them out.
Good luck

Well this problem has returned, was fine thru summer, now its cold and happening again. just posting to bring this to top in case someone has solved this. Last I left this issue, I was going to look for source of high LFT, running 15 at idle, in hopes the vacumm leak that is causing that is the source of intermitant rough idle.

I have the exact same rough idle problem with my 2004 Impala SS... Just checking in to see if anybody has anything new to add. I took my car into the shop and they told me it was the MAF sensor. And that after I changed it I would have to take it to the dealer to have the computer flashed. Is there any truth to this? I have replaced the MAF (Mass Air Flow) sensor and it seems to work a little better (not as rough). I am wondering if having it flashed would help at all.. I hate going to the dealer! :biggrin:

Thanks

When you are completely frustrated with this issue, please do what was suggested by a senior mechanic by the name of Steve in Minnesota somewhere on the internet. The problem is related to the cooling system, and requires you to remove the radiator and/or the condenser for a full cleaning of the surface and fins. The radiator and condenser needs to be completely removed or provisions need to be made to thourghly flush out any accumulated dirt, cottonwood, foreign matter, ect., from the fin material. I for one was completely frustrated with this hot start issue on a 2002 Windstar with a 3.8L engine that would run terrible for 30 seconds to one minute after it was started following a hot soak of 10-20 minutes stopped while warm. The vehicle was tuned up with new plugs and wires, new coil pack, computer scan and reset, different fuel grade and supplier, you name it it was tried! This repair did correct the rough running after hot soak instantly from the time the cleaning was performed. I did remove the radiator and condenser(need to remove refrigerant and plug fittings) from the vehicle(I am an hvac tech/mechanic part time) so this was easier for me to do, but if you can't/do not want to remove the condenser, then it is imperative that provisions are made to make sure that all surfaces of the radiator and condenser can and will be completely flushed and cleaned thouroghly! I did spray all surfaces on both sides of the condenser and radiator with "Purple Power" cleaner available from my local Dollar General store. This "Purple Power" is similar to Castrol brand "Super Clean" but at a reduced price. These two cleaners have high amounts of cleaning power and worked extremely well for me in removing the dirt and crud that had accumulated in the condenser and radiator. Upon first look it does not appear that there is much stuff clogging up the fins in either the radiator or condenser, but when you start cleaning and flushing out you will be amazed with what comes running out I know I was! Once cleaning was completed I re-installed both radiator and condenser and refiled freon and anti-freeze, tested and never had another hot start issue to date! In retrospect I really didn't think this would cure the problem, but after trying everything else it did really work! Although the vehicle here is a Ford Windstar minivan, I have no doubt that this repair may help cure other vehicles ailed with this seamingly random hickup in drivability that is almost nevery re-producable for your local garage! For me I would like to thank Steve in Minnesota a master automotive technicial at a Ford dealarship for the advice to clean the radiator and condenser, it did work for me!

In my Taurus 2002 with the 3.0L OHV Vulcan engine, I had the "Hot soak start rough idle" intermittent issue. It happens when I start my warm engine, it runs rough for 30 seconds and I even feel a 2 seconds delayed accelerator response like if I had low fuel pressure. Rough idle is about 400-650 rpm.

I also had once check engine light and the codes P0300 and P0316 and they clear up after 5 minutes of driving.

I search info thru Ford TSB, and I found a TSB for that issue saying that idle can be rough after a hot soak start and there's nothing we can do for that.

TSB numbers are 02223, 15680, 15745 and 15915:
http://www.aboutautomobile.com/TSB/2002/Ford/Taurus/Gasoline+Engine (http://www.aboutautomobile.com/TSB/2002/Ford/Taurus/Gasoline+Engine)
http://www.automd.com/tsb/bulletin_b169122/ (http://www.automd.com/tsb/bulletin_b169122/)

The cause of the problem is when fuel remains too long inside hot injectors and fuel rail, it becomes too hot and vaporises within the injector and rail, especially with very volatile winter-blend fuel when it's relatively hot outside for winter, so it causes vapor lock and fuel starvation because fuel has more difficulty to flow because of the vapors, so that causes misfire because of the lack of fuel injected, until vapor is cleared from injector or condensated and cold liquid fuel arrives and fuel debit increases.

I also search more info thru the internet, and I found an theory (and cure) that confirm what Ford TSB is saying in a Jeep forum:

"This is a known problem with the 2000-2001 XJ. If you search "heat soak" or "rough idle after hot start" you will see many having the same issue. The problem is that the engine gets very hot when it bakes under the hood, which makes the fuel in the injector (typically the #3) pretty hot also. On a hot start the fuel in the cylinder won't ignite correctly and cause the misfire until new cooler fuel is brought into the cylinder. This is why the problem happens most often in hotter weather or after running the engine awhile, and the miss usually goes away after revving the engine.

The fix is fairly easy... My 2000 had this same problem last summer.

I had it fixed by the dealer because they told me it was a recall, although some tell me the recall was only on Wranglers. Either way, the problem hasn't come back yet. What the dealer did was put a heat shield around the #3 injector, to prevent the fuel from heating up and causing the missfire (http://viglink.pgpartner.com/rd.php?r=402&m=1117852305&q=n&rdgt=1365514598&it=1365687398&et=1366119398&priceret=21.50&pg=~~3&k=7de5ed960c210c32427a06376a3a28ac&source=feed&url=http%3A%2F%2Fwww%2Eamazon%2Ecom%2Fdp%2FB002LVY YYE%2Fref%3Dasc%5Fdf%5FB002LVYYYE2460773%3Fsmid%3D ATVPDKIKX0DER%26tag%3Dpg%2D304%2D01%2D20%26linkCod e%3Dasn%26creative%3D395097%26creativeASIN%3DB002L VYYYE&st=feed&mt=~~~~~~~~n~~~). I'll try to put up some pics of it."

In these pics, it is the tan shield surrounding the injector. Might be kind of hard to see.

http://i926.photobucket.com/albums/ad106/jeepkid03/Mobile%20Uploads/0317101815-00.jpg



http://i926.photobucket.com/albums/ad106/jeepkid03/Mobile%20Uploads/0317101816-00.jpg

Here's the official TSB from Jeep: http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf (http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf)

Jeep has the "Rough Engine Idle After Restart Following A Hot Soak" problem.
Jeep has the same problem as Ford, just like other car manufacturers like Acura, Honda, Volkswagen...

They said that the problem can be aggravated by the use of fuel contening ethanol.
Because ethanol fuel has a lower boiling point, thus it's more volatile than pure gasoline.
So I suggest to NOT use fuel blend with 10% ethanol if you have the choice.

They also explain how to fix this issue. They suggest to install an insulator sleeve wrapped around fuel injectors like the Jeep owner done above.
Solution mights works with Ford engine as well.

I suggest to wrap a cutted insulator sleeve or rubber hose around all injectors and fuel rails.
Then attach the splitted sleeve with tape or tie-wrap.

Heat is irradiated from lower intake manifold to fuel injector and rails, causing the injectors, rails and the fuel to be very hot after a long drive.
So when vehicle is parked for 10-20 minutes, the fuel remained in hot injectors and rail become very hot and vaporises causing rough idle.
Wraping insulator sleeve (heat shield) around the injector protect it against heat radiation.

Taurus 2002 with 3.0L OHV and Windstar with 3.8L engines have metallic fuel rails. Metal is very heat conductive, so it become hot when it's close to heat radiation. Metallic fuel rails are close to hot lower intake manifold of the engine so they become very hot.

I also found a TSB for a similar issue for Windstar 1995-1996. TSB# 97212 http://www.automd.com/tsb/bulletin_b18570/ (http://www.automd.com/tsb/bulletin_b18570/)

The difference between this TSB and the Taurus' TSB is that engine doesn't start at all after hot soak.
They said it happens in freezing temperature, I assume it could be because of the use of winter-blend fuel.


Like perrytime said, the problem is vapor lock. It happens when we use high volatile winter-blend fuel and we start the engine when it's very hot.
Also sometime after a long drive into traffic, because engine heats up and fuel debit is low.

It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump because it pumps less liquid to maintain pressure and fuel has more difficulty to move, causing loss of feed pressure to the fuel injectors.
There's more resistance in fuel rail because of the fuel vapor pressure. Fuel should circumvent the vapors to arrive at the injectors. The fuel flow is reduced.

http://en.wikipedia.org/wiki/Vapor_lock (http://en.wikipedia.org/wiki/Vapor_lock)

A vapor lock is more likely to develop when the vehicle is in traffic because the under-hood temperature tends to rise. A vapor lock can also develop when the engine is stopped while hot and the vehicle is parked for a short period. The fuel in the line near the engine does not move and can thus heat up sufficiently to form a vapor lock. The problem is more likely in hot weather or high altitude in either case.