I just finished starting up my car this morning to try to figure out why its acting up, but I am completely lost. It is running very odd, and I can't even begin to imagine what would cause it to run like this. When cold, it will idle ok, but the rpms are very slow in going back down under deccelaration. When it warms up and the rpms come down like they should to like about 700, it will start shaking. When changing gears, or in neutral though, the engine will die down to about 500 rpm, hang there for a moment, then surge back up to like 1000, and then settle at like 700 or so.

The engine is really hot now, so I'm going to let it cool before I start checking things over. I don't know what to look for though. I don't think a vaccum leak would cause this. I'm going to check the plugs, cap and rotor, and from there, I don't know where to go.

I recently swapped from auto to manual, but I can't see how this would relate to this problem. I replaced the automatic chip for one off a manual car, so that shouldn't be an issue.

Anyone have any ideas? I'm lost.

 

92,

Most often, "crazy" idle can be attributed to a worn or sticky throttle body, or a sticky or dirty IAC. Clean the TB and check the throttle plates closely for interference at the edges of the bores. Check the amount of play in the throttl shaft. Remove and disassemble the IAC, and clean it thoroughly, as well as the recess that it screws into.

When you reassemble, set the TPS and minimum air position, and your "crazy" idle may be a bit more sane.

 

Ok, I finally got a chance to take a look at the car yesterday, but I still don't know whats going on. I removed the IAC and sure enough, it was dirty. I cleaned it (wasn't sure with what, so I just used gas), and checked the throttle body. That was clean, and the throttle plates opened and closed smoothly. I started the car back up, and there was no difference. I was curious as to what would happen if I disconnected the plug that goes to the IAC, even though it doesn't sound like a great idea right now. Well, the rpms would stay at wherever rpm you would rev the engine up to and not go back down. Ok, so that was pointless.

I decided to check a few things while I was under the hood, and one of those happened to be the egr valve. Accoding to Chiltons, the diaphragm should move freely. I could make it move, but it requires alot of effort. I checked the vacuum line for vacuum, and its fine. It doesn't have vacuum at idle, but it does under an rpm increase. I hooked the line back up to the egr valve, and I could just barely notice any movement in the diaphragm when the engine accelerates. Is that normal? How much is it supposed to move?

Oh, I almost forgot. How can I find out if the IAC is bad or not? I realize I can probably figure that out with winALDL, but I don't have a laptop, or alot of time to learn about all that right now. That is something I'm going to get into later on though.