RT/TT Rough Idle

[ilian51378]

Hey guys,

I have a friend whose RT/TT idles rough and he can't find why that is happening. When idling, the car is shaking and so on. When he hits the gas and goes over 2000 RPM, the issue goes away... He has taken the car to several different shops where they have diagnosed it, but could not find anything wrong with it. His problem is that he lives in Eastern Europe and there are no mechanics that know our cars well enough there... He has replaced the ECU with a rebuilt one that was tested and worked good, but that did not fix the problem. The compression is great and the diagnostics show that everything else is fine. Could it be his air filter (MAS?) sensor? Dirty throttle body? What else could be causing that? Any input is appreciated. Thanks!

[Mike-92RT]

a bad MAS would make the car run like complete shit. But if he wants he can unplug the MAS and if it runs better then when its plugged in, theres his problem.

It could be a vacuum leak, it could be a dirty IACV, it could be a dirty TPS, maybe even a boost leak? i dont know if a boost leak would cause rough idle or not.

To test for a vacuum leak, spray intake cleaner all around your intake/throttle body/air intake pipe/vacuum lines, and if the engine revs up, then theres your leak.


could also be the sparkplugs or coil packs. Tell him to get those checked.

[93STLTH]

A simple thing to check is the throttle body gasket. The little tab on the gasket should be towards the firewall, not the front of the car.

[marshallh]

IAC, you can check with a multimeter here (http://www.stealth316.com/2-isc-iac.htm)
Vacuum leak somewhere
FIAV in throttle body

[Emilie@GZP]

does it run better with the MAS unplugged? what year is the car?

[ilian51378]

Thanks for the input guys! I forgot to ask him what year the car is, but I will and I will report it here. I don't think he has tried to run the car with unplugged MAS, but I will tell him to do it...

[ilian51378]

Okay guys,

I found out some more info that I didn't post... Well, when my friend bought the car, it was running on four cylinders. When he changed the ECU, the car started running perfect. However, after he changed the timing belt, the above described issue occured... :rolleyes3:

[Boomer3000]

Then timing might be off... Double check that. If your lucky no damage has been done yet.

[Mike-92RT]

agreed /\

when timing these engines, its hard to keep all 4 cams in place while tensioning the belt, so one of them could have came off mark? Cam lockers help BIG time, and also the tensioner pulley tool that 3sx sells.