Intermittent Rough Idle

[JBurt]

Hey guys. So my father in laws rig is an 98 with an intermittent rough idle. It happens at several different speeds, engine loads, and temperatures. The funny thing is that it doesn't throw any codes.

I'm headed over later today to check for vacuum leaks, clean the maf, and look at the ecu readings while it is having the problem.

He's taken it to the stealership before and paid about $900 for them to tell him they couldn't replicate the problem. They did replace the plugs and wires. I don't know what else they did though.

Any ideas? Most of the threads I've read talked about plugs, wires, and misfire codes.

 

[LittleCaesar]

I'd start with cleaning the TB and IAC. +1 with the vacuum leak check.

 

[MarkinWMich]

Because it appears to be "random", my guess would be an intermittent vacuum leak. They can be a real "bugger" to track down. Any tiny crack in a hose or a connection that reveals itself from engine vibration, temperature expansion or contraction, etc. can be the culprit.

My '89 Mustang used to do this when the PCV system got a little "gunked up" and the vacuum from the engine would suck oily crud into the upper intake manifold. Might be something else to check out.

If it isn't "throwing codes", then it isn't likely to be an electrical or sensor issue.

 

[JBurt]

Good idea with the pcv

 

[JBurt]

Well I got over there and he had decided to take it back to the dealership. This time they replaced an injector. We'll see if it stays away. For the price they charge I hope it does

 

[JBurt]

Just to follow up there have been no problems after replacing the injector.

 

[19963.4lsr5]

Sometimes it's worth having a spare set of injectors to be able to have them professionally cleaned and matched.