Hot soak start rough idle

[perrytime]

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.

[perrytime]

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.

[wiswind]

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.

[Ed_Strong]

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!

[kevink1955]

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??

[perrytime]

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.

[wiswind]

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....

[dps1250]

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.

[perrytime]

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.

[dps1250]

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

[perrytime]

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.

[perrytime]

this post leans to my theory

http://www.automotiveforums.com/vbul...d.php?t=516738

[perrytime]

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.

[perrytime]

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.

[perrytime]

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