I got into a small accident and had the car fixed at the body shop. It was working fine after the accident and needed miror body work for front end. After picking up the car from the body shop, my idle keeps on dropping at 400-500rpm and then jumpin bak to ~600 after little while. While I am driving, the car is fine. What you guys thing can be the problem. The body shop guy swears he had not touched nething in the engine. Rpm drop occurs while i m in park, rev or drive. Please help me out..thanx in advance

 

My problem was spark plugs. I had the same problem as you. When were they last replaced? You clean your throttle body also?

 

I replaced it about 25-30k miles ago. i have 77k miles on the car now and i blive i replaced it at 45-47k miles. I cleaned out my TB 1.5 yrs ago. it is weird for the problem to occur out of nowhere. BTW car is 95 auto GLE.

 

Try cleaning out the IACV (Idle Air Control Valve), this helped my low idle problem. Also, clean out your throttle body again. A year and a half ago is a while back.

You may want to check the ECU for stored codes as well.

 

What kind of Spark plugs did you use? It could be time to replace them depending on what kind you have.

 

clean your TB

 

Check for air leak?

 

I was having the same problem. I cleaned my IACV and my car is back to normal.

 

Got it! one of the hose for air intake was lose.

 

I'm glad that you found what the problem was .

 

 

I'm having a similar problem... when I start from a cold engine, my rpm goes up to 1k then drops to like 500 or sometimes below that then back up to 1k.... it doesn't fluctuate or anything... i guess my crank has a hard time turning?

Anyway I was reading this thread and I was wondering if anyone can tell me how to clean the IACV (Idle air control valve) and also how to clean the TB.

I'm not too sure where they are in my car (1997 Max GLE AUTO).

Pics would be helpful... Much appreciated...

 

You can got to www.motorvate.ca to see how to clean the throttle body.

How to clean IAC valve

Tools needed:
10 and 12 mm sockets
3 inch socket extension
universal joint (swivel pivot socket thing)
12-inch rachet (a short rachet may not work - need something to apply a lot of torque to loosen the bolts
Philip's screwdriver
rag
throttle body cleaner

1. Unplug the 4 connectors from the IAC assembly. Undo the hose that connects teh IAC to the intake assembly.

2. The metal bracket holding up the gray-colored connector is blocking one of the IAC mounting bolts. Using a 10mm socket, remove the bolt that holds the metal bracket. The bolt is just below the purple connector - you have to twist your head and crane your neck around to see the bolt.

3. Remove the 3 mounting bolts using the 12mm socket. The lowest bolt may require the Universal joint.

4. Pull out your IAC valve and clean it w/throttle body cleaner, rag, and old toothbrush.

You may even want to separate the plastic valve to clean it more thoroughly. Use a philip's head screwdriver, but make sure it is a snug fight. It's on there tight and if you don't have a good fitting screwdriver, you could ruin the screw head.

Reinstallation is just the reverse of these steps. It may be easier access to the IAC if you remove the whole air intake assembly, but it's not necessary.

 

Just adding to the discussion, but I'm about to clean my IACV and noticed that a gasket may need to be changed. For those who cleaned the IACV did you change the gasket or use the old one and if you did what is the part number?

 

Normally when we get a car in our shop one of the things we do is disconnect the battery when the car is being worked on. Helps prevent damage to the electrical system, especially if were welding.

This is a statement from the Haynes service manual:

If the battery is disconnected for a long period of time the ECU will loose stored engine operating parameters and need to relearn itself. During this time the engine may run poorly and experiance an abnormal idle.

This is not the same thing as resetting the ECU via a scan tool or the limit switch on the side. It will take a short period of normal run times for this to correct itself. Give the car a week or two and see if everything goes back to normal.