'93 Caravan - Odd Idle, Dies in gear

[TrueLyFE]

Hey all.

I recently aquired a '93 Dodge Caravan 3.0L, that seems to drive well, except for an odd idle issue. When cold, it doesn't idle very well unless I give it some gas... when warm, it usually idles, but the speed is very erratic. When putting the car into gear, it will usually die - if I give it a tap of gas while holding the brake then it will stay in gear, but eventually dies.

When driving at normal speeds - anything from no gas to full throttle - it drives fine. It's only the idle.

I did some normal maintenance - spark plugs, wires, fuel filter. I tried to see if the AIC was the problem but I don't know how to test that (I did clean out the throttle body and the AIC port area, though). I did verify (at least as well as I can tell) that the EGR works (moves), but until I get a vacuum tester I can't tell if it is leaking. Any quick pointers on that would be a help. I wouldn't think fuel pressure would be the problem since it seems to drive well.

So, based on other posts, I am pretty much looking at the likely culprits being the AIC or the MAP sensor, correct?

Any ideas?

[jsinton]

I had the same problem where it didn't want to idle when it was cold. It ran fine other wise. If I took my foot off the gas at a light, it might stall. Turned out that my battery was weak because I had a voltage leak when it was parked and off. It was draining the battery to the point where when I took my foot off the gas the alternator couldn't keep up and the car would stall because it was trying to charge the battery too much and there wasn't enough juice in the system.

Once I found the voltage leak and charged the battery, it never did it again.

Make sure your battery is good, if possible have a charge done. If you think your battery is old and due to be replaced, then go ahead and replace it as this is common sense anyway. A weak battery puts additional load on the electrical system and can burn up your alternator or screw up other electrical parts. It's especially important in modern cars because of the heavy load they put on the electrical systems.

[TrueLyFE]

Thanks.

I forgot to mention, I did test the battery - voltage is fine. Alternator charges fine. Over 13.8v at the battery.

I replaced the MAP sensor; it seemed to boost the idle speed a bit when not in gear and flatten out the dead spots, but it still dies in gear. I also replaced the PCV. Sigh...

EDIT: Cleaned out my EGR valve tonight; it's not perfect but certainly less carbon buildup. I got the valve portion as clean as I could get it with a knife, an icepick, compressed air and carb cleaner. I'll slap it back on tomorrow without the transducer hooked up and see if that improves my idle condition.

I also have a feeling the AIS works, since after I let off the throttle, it holds a higher RPM for a little bit before dropping down. Could still be defective - dropping down too much - but just thought I'd like to point that out. I'll keep you all (the very few who have even bothered to read this thread) up to date

[TrueLyFE]

Replaced my cleaned out EGR valve (and did the tube while I was at it, along with the passages as best as I could) with new gaskets. If there was a leak, it was really tiny - the car still doesn't idle well in park, though it doesn't want to die as easily as it did before. It still dies in drive.

The only thing I can think of to replace is the AIS, which was what I first suspected. Is it normal for these vans to take a little while to return to idle RPMs after letting off the throttle? What else could be the issue?

I was going to time the car today, just in case it was that - but Harbor Freight, though saying they had dozens in stock, couldn't find a single timing light. I am going to order one and time the van as soon as I receive it, just in case THAT is the issue.

Edit: I probably didn't mention - the guy who sold me the car gave me a new TPS, since he said the old one was dead. I installed it, and I just checked the voltage range - it goes from 1.01v to 3.8v. Don't think this is the problem either.

[doratheexplorer]

Originally Posted by TrueLyFE

Is it normal for these vans to take a little while to return to idle RPMs after letting off the throttle?

My '95 3.0L (114K miles) will take time to idle off throttle, typically during warmup. When warm and driving, it usually drops down to 800rpm, but much slower than my '04 Honda.

I have a slightly erratic idle, but fortunate enough to have intermittent stalling. I've checked, cleaned and/or replaced pretty much everything except the MAP sensor (waiting in a box in my tool chest) and the ignition coil.

When I checked the timing, it was dead on. Here's what hasn't worked for me:
(a) I rebuilt the alternator & new 1000 amp battery (starts up nice, though!)
(b) purge valve solenoid (waste of $$, other one was fine)
(c) cleaned & tested throttle body, AIC, EGR (nothing different)
(d) TPS, like yours, within spec
(e) I stethescoped injectors & soap checked the hoses (nothing but clean hoses)
And now, according to your results with the MAP sensor, I might be adding that item to this list.

Keep us informed of your progress.

[TrueLyFE]

Alright.

Reset the throttle screw (it was all the way in) and timed the car today - it was way off. All timing it did was make my car die easier. The throttle screw is almost all the way back down now, and it idles though the idle still varies (of course, better with the new MAP sensor). This is while warm. I can't begin to imagine how bad it'll idle now when cold...

Old distributor cap and rotor were a little worn, I replaced those too today. No change.

I think the only thing that I haven't really checked would be the AIC... or the computer? :/ I'm pretty much stuck. What the hell? This thing is turning into a money pit, very fast.

doratheexplorer, you didn't actually replace your AIC, did you? I am going to get one for a decent price here soon and try that. If it doesn't fix it, I will be able to return it

[RIP]

If the AIC doesn't help you might want to add a vacuum leak at the intake manifold gasket to your list, if you haven't already. Spray brake cleaner around the base and listen for an rpm jump, if you can keep it idling. Is the hose to the brake booster in good shape?

[Stretch58]

Look at the vacuum hoses on the various components such as the PCV etc., they should not be hard as a rock. New ones are supple and will allow a good seal, old ones through heat, etc. will get hard. Could be a combination of more than one small leak.

[doratheexplorer]

Originally Posted by TrueLyFE

doratheexplorer, you didn't actually replace your AIC, did you? I am going to get one for a decent price here soon and try that. If it doesn't fix it, I will be able to return it

I didn't replace the valve, but I was able to test its operation using a diagnostic scanner. If you have success with replacing yours, I will replace mine ($55 Autozone).

Thanks for the reminder, Stretch58. I replaced almost all my vacuum hoses last fall...forgot the PCV hose! Mine feels like it's made from pencil lead.

[TrueLyFE]

Hey all. Thanks for the vacuum advice.

I replaced a number of vacuum hoses, but some (like for the brake boost) seem original. It still seems pliable and well sealed, but can't be certain for a leak until I check. I didn't know how (haven't had vacuum problems with a car yet) - Brake cleaner, 'eh? I'll try it tonight on the hoses I haven't replaced and on the intake (it'll idle decent enough if the engine is warmed up). PCV, MAP, EGR all have new hoses. Fuel pressure regulator and brake booster don't.

This weekend I will pull 3 or 4 AIC valves from cars over at the bone yard. Surely one of them will work if the AIC is truly the problem. =)

I'll report back tonight on the vacuum situation. Thanks all.

====

EDIT: All vacuum hoses in the van are new now. No change.

Tried the brake cleaner trick. Nothing.

At least I don't have to worry about brake vacuum now, sigh.

[Rawtorque]

2 other things to try:

1. Mass Air Flow sensor (MAF): This is in the air intake path, and is not the same as the MAP. These can cause weird idle. One way to test it: While idling, tap the MAF with a screwdriver handle. If the engine dies, then the
MAF is bad.

You can also have it checked on a scope by a Mechanic.

2. Clogged fuel injectors/fuel filter.

[TrueLyFE]

Alright, uneventful update.

Changed out the AIC with one I pulled from some '95 2door convertible at the junkyard, 120k miles... no change in stalling, but the idle is smoothed out significantly. It tries to idle higher now (probably a good thing, as the timing is retarded again and the throttle screw is in nearly all the way - it gives me some room to adjust). As in, it doesn't idle all over the place, although it is still dying as easily as it did before.

I'm going to pull the battery cable and try it in a bit, and let you know if anything changes. If nothing does, however, what's left to look at - the fuel system? Fuel pressure regulator or return line? Pump perhaps, although fuel delivery seems fine at cruise speeds?

If you think it's going to be the fuel system now, I'll get a gauge and attempt to diagnose where it's coming from. I was going to get the fuel pressure regulator off of that car too, but I forgot

====

Edit: Rawtorque, this car doesn't have a MAF. Also, as I said above, I replaced the fuel filter. It seems to want to idle, though, and it does when warm...\

Also, the battery cable did nothing - the car still dies.

====

Edit 04/01: Alright, I think I've narrowed it down to the fuel pump. Why?

Well, I've replaced all the vacuum lines, verified or replaced all the emissions stuff that would be relevent, have a new MAP, TPS, AIC... and I just got done with the fuel pressure regulator. The return line seems fine too, not clogged. So...

Basically, when driving, it seems to drive alright - but what I just noticed, when holding the throttle high, the engine speed varies like crazy. Also, I wouldn't doubt at all that the fuel pump on this van is original - and 160k miles is probably long enough for it to live, right? It's also fairly loud, not as loud as GM pumps when they're about to go out but I certainly hear it in the car at idle.

So, this next paycheck, I'll be putting in a new pump. Couldn't hurt, right? I just hope this is it. Otherwise, this car is going - I don't know what else could be wrong with it.

[doratheexplorer]

Originally Posted by TrueLyFE

...I'll be putting in a new pump. Couldn't hurt, right?

There's a real good chance that a new pump won't fix the problem. It will, however, put a good dent in your wallet ($150 - $250).

I recently read that the coolant temperature sensor (~$40) might be the problem. It's next door to the water outlet housing. When it goes out, the computer doesn't realize the need for a high idle through the warm up cycle. (Link attached)

http://www.stretcher.com/stories/07/07apr02e.cfm

[TrueLyFE]

Hm. It's just that the engine RPMs are erratic, even with some throttle...

But when the van does warm up, the fan kicks on / off as necessary. The idle still isn't perfect, either, and the van will still stall in gear and not moving. Is the CTS a common enough issue with Chrysler vehicles?

[ronmar1]

Originally Posted by TrueLyFE

Hm. It's just that the engine RPMs are erratic, even with some throttle...

But when the van does warm up, the fan kicks on / off as necessary. The idle still isn't perfect, either, and the van will still stall in gear and not moving. Is the CTS a common enough issue with Chrysler vehicles?

The Coolant Temperature Sensor is a common problem and would have been the first thing I would have checked. It will definately cause Idle problems.
Ron