I've been having an ongoing problem where my car won't hold a smooth, consistent idle when sitting at stoplights, drivethrough, ect. When I first start up the car, it idles really high until it gets warmed up (about 900-1000 RPM), and then will drop back down to about 600 RPM. The problem is, when I sit at a light for more than 15 seconds or so, the car will start to shake badly every few revolutions, the RPMs will drop down to about 400 and then it will go away until the next few revolutions and then do it again. It gets so bad at times (when I have to wait for an especially long light) that the car has actually stalled out while I'm waiting.

I've looked all around the engine bay for vacuum leaks and I actually did find a couple that were probably contributing to the problem--I found one that was hidden underneath the air cleaner which is attached to the manifold itself... it was completely unattached). However, the problem is still there. I'm getting aggrevated because the car will act nice and drive like it should until I have to stop for something for more than 15 seconds, then it starts shaking and idling rough, even sometimes stalling.

Any other ideas what might cause this other than a vacuum leak somewhere? And are the any particular places that are notorious for creating vacuum leaks? I've learned that these LG4s are one of the worst engines when you are trying to find vacuum leaks because there seems to be dozens of these lines to track down.

Thanks for any help/suggestions.

 

If you can get the thing idling funny in your driveway, in park, start pinching vacuum lines. If it instantly clears up, figure out that lines purpose etc.

Also, use a propane torch, unlit, and just let it blow propane towards problem areas. If idle speed picks up, bingo. Try intake-cylinder head mating surface, base of carb, egr area, etc.

Usually a vacuum leak raises the idle speed though. Your problem might be something else. Not sure what off the top of my head though. How's the ignition system?

 

Ignition is fine. Timing is good.

I started tinkering around today with the various vacuum lines in the engine bay after posting this, pinching just about every single one I could find and still having no luck.

However, I did notice something that didn't get my attention before. When I put the car into drive and let it idle, I heard a clicking noise that sounded really out of place... way too loud and never ending. Further inspection led me to figure out it was the EGR solenoid making the clicking sound. I unplugged the electrical connector from the solenoid, and although the engine didn't seem to care, the clicking noise went away. Once I put it back in, the noise started back up again. Once the car is in park, it does not make this noise.

I tried inspecting the EGR valve itself, and it appears to be in good working condition. The vacuum line to the EGR itself was not creating any suction when I pulled it off, but as far as I know the EGR barely does anything when the car is just idling.

The clicking sound is what concerns me. I've never noticed this sound before, and it's quite loud... loud enough to hear it clearly over the rest of the engine which is pretty loud itself. Should I look further into this, or is it normal for the solenoid to make this noise?

 

No one knows if it's normal for the EGR solenoid to click like this?

 

Are you sure it isnt the MCS on the carb ticking? (it's supossed to and is loud)

The EGR sensor cannot tick as far as i know.

What is your TPS sensor reading at idle? That would be where i'd start my trouble-shooting. Also make sure your choke it operating properly.


Try pinching off lines like Sonix said, but he's right about the leak, it would cause a high idle if it was a small leak. A huge amout of unmetered air, on the other hand, would make the engine impossible to idle.

 

Alright, a little update on this...

First of all, I'm positive that it's not the MCS clicking. When I unplug the EGR solenoid connector, the clicking stops and then I can hear another (faint) clicking from the MCS. I plug the solenoid back in and the horribly loud clicking returns.

The car has also started idling really high (something it wasn't doing before), and when I shut it off it diesels really bad sometimes. This just started happening about a day after I posted this and noticing the EGR noise.

How would I go about checking my TPS? It's something I've never done before.