Okay all you mechanics, you've got to help me figure this one out. A while back I posted a topic thinking I had a vacuum leak... while I haven't found the source just yet, I thought of something else that may confirm/deny the vacuum leak. After the car is warmed up (i.e., driving for a few minutes), if I sit at idle IN GEAR (say at a stoplight), the tachometer usually hovers around the 300-400 RPM range the idle is very lumpy and "chuggy". (Sorry for the technical adjectives). It will usually continue to drop down slightly and then come back up but it always stays below 500 RPM. Is this normal? What should the in-gear idle speed be?

I should mention that this is without any accessories on.

Thank you in advance for any suggestions.

Mark

 

in gear idle should be around 600 rpm, 750 in park, try using higher octane gas as that effects idle of the engine, also i had a similar problem with a vaccume leak that i found connected to that charcoal canister, i dunno if you have the same problem but it might be?? good luck man

 

91,

No, idle RPM with a warmed engine should be closer to 650 RPM in DRIVE. A relatively small or minor vacuum leak will generally cause an engine to idle higher, but rough. A massive leak will cause low RPM and/or stalling.

What engine do you have?

Do you have an idle vacuum reading?

Have you cleaned the IAC anad throttle body?

 

No, my next step is to replace the O2 sensor and check the IAC. I still think I have a vacuum leak though (because of problems mentioned in my previous post). It surely wouldn't hurt to do the O2 and IAC in addition to fixing the vacuum leak. Thanks.

Mark