90 Caprice Idling Issue

[CapriceCop]

I am having problems with my idle when it is raining. It will idle erratically: almost dead to high idle. Also, I checked the codes and I have code 51: ECM problem. I had thought that may be an exposed wire was becoming shorted with all of the moisture underneath my car. With a little research, I found that a similar problem can be caused by a cracked intake manifold gasket. Which did seem to make sense if water is getting on top of the engine while I drive. Now that it is dry, it idles nicely.

Any opinions before I tear everything off the top of my engine this weekend? Also, will I be able to reset the code or is that problem permanent?

Keith

[HLandin]

The codes should remain in your computer until you reset it by disconnecting the battery.

[CapriceCop]

That is what I had figured. Is a code 51 indicating a bigger problem or just a typical computer issue?

[Cyrix_2k]

Try cleaning the throttle body. Mine idle's low when it's cold out because it's dirty and I haven't gotten around to cleaning it yet. It actually idles so low that when I stop, the voltage gauge drops since the alternator's not producing enough current to run the car!

[CapriceCop]

Well the cold definitely isn't the problem. I get the typical high idle when the temps were around 50 yesterday. It just seems to happen when I drive around in the rain but not immediately. Which eliminates high humidity. It is more of a soaking problem after driving around on the wet roads.

[CD Smalley]

Try this... Get a can of carb cleaner. Let the car be cold. Start it and let the idle settle down. Then spray the carb cleaner at the base of the TBI unit right where it meets the intake manifold. If this has any effect on the idle speed then you need to replace the gasket between the TBI and the intake. $2 part that can cause a lot of problems.

[silicon212]

Another possibility is the IAC solenoid. Carb cleaner can help here, too.

[smokinhydes1]

How old are your plug wires? That sounds like a "Classic" secondary ignition problem. IAC won't produce rough running. Code 51 can often be set when the engine drops below 300 rpm but is still running : this is usually due to low voltage output coming from the alternator getting the computer "confused".

[CapriceCop]

This is the list of all of the things that I have replaced in the last year:
MAP sensor
Plug wires
Plugs
Distributer and Rotor
Vehicle Speed Sensor(check engine light indicated that one)
O2 sensor
Ignition Module
Fuel pump and filter
Intake manifold gasket (yesterday)

The IAC seems to be working properly. I have adjusted it to pick up the idle.

Unfortunately, last night was a dewy type of night and the car still idles erratically. My last approach is to find all of the ground connections and redo them and look for obvious electrical shorts. This is getting frustrating but has been informative on car repair. Is there anything else NOT on the list that controls the idle? The ECM was swapped at the repair shop to see if that had anything to do with the idle, but nope.

[smokinhydes1]

Wucking FOW! You HAVE replaced everything. Ok, then have you tried the carb cleaner advice? You can also put a hose fitting on a propane bottle and feed that down the throttle body when the idle is erratic....if it smooths the idle then you do indeed have a vacuum leak. I run an automotive repair facility, I can pull up all the grounds and other info you may need on Mitchell. Now that you told me all this other stuff, I can see why you're

[smokinhydes1]

Two other thoughts, was the ECM AND the Prom replaced, or was the old Prom moved to the new ecm <Hmmmmm>, and did you replace the distributor itself or only the cap? I have in two instances seen this be the distributor. When I compared the old to the new, even completely torn apart, I could see NO difference. But the new distributor fixed the problem.

[CapriceCop]

Oops. Yeah distributor cap. I had been told about the distributor giving problems but they are expensive, so I tried other ideas. The thing is I can go outside right now while it is dry and run the car without problems. The problem arises when the dewpoint has been reached or when I drive through water. What I have considered is taking a spray bottle with water and spraying different parts of my car: back of engine, front, random connections underneath,.... To try and replicate the problem.

What I know about the ECM is that the guys popped in a "new" ECM and nothing changed. I don't know if that meant "new" everything.

The propane idea is a new one. I think I can borrow a propane blow torch and try that idea. I tried spraying carb cleaner around the base of the TBI with no effect as well.

Thanks for the ground info, I might be taking you up on that soon.

The funny thing about all of this is that the car is old, worn,(173K miles), damaged and we are planning on selling it soon. I just want to find out the problem so I can say I haven't been beaten!!! FREEDOM!!!!!

[CapriceCop]

Well, I may have found the culprit. It is called an Air Charge Temperature Sensor. I would like to add that according to the parts store computer, my car does not have one of these. Go figure. Does anyone happen to have the operating specs for one of these, as in the ohms of resistance at a certain temp? I would like to check the old one to the new one just to be sure. Man is it good to be idling right again......