All of a sudden yesterday sitting at stop lights, or just idling, the idle RPM on my 2000 Max would all of a sudden drop to 500 RPM with a slight noticeable shaking of the engine... from its normal 650 idle speed. Any ideas what I should clean or check to fix this? I"m going to try cleaning the MAF, TB, check vacuum hoses... etc. It just all of a sudden started doing this.

The car drives normal otherwise and when I come to a stop it'll idle at 650 for a bit and then it'll drop down to 500. weird...

anyone have experienced this?

My coils have been replaced. And so has the spark plugs.

 

Sounds like the AC compressor kicking in.

 

nope, failed to mention no ac running. When the ac is on, the idle actually supposed to speed up.

But I've fixed the problem. It turns out I had forgotten to put the oil filler cap back on two weekends ago when I changed the oil. The bad but not too bad is I drove 28 miles with the cap off and good thing it didn't fall and get lost. No oil splatters either... I changed the oil 2 Saturdays ago and I guess forgot to put the cap on. But the car sat until this past Sat when I drove it and yesterday and today. The idle drop started this past Saturday.

So, that was the cause then. Man I was wondering what's up. Good thing I wasn't driving in too dusty or rainy weather this past couple of days.

 

i was going to say clean your IACV

but no oil filler cap??

 

Lucky you with just an oil filler cap.

I just had to replace my TPS and IACV.

 

So replacing the filler cap fixed the idle problem... anyone care to explain how this works?

 

I got similar problem, but with oil cap on. lol
Here's what happens: when the engine is cold I have to keep it over 2500 rpm for 15 - 20 seconds after it's just started. Otherwise it will stall within those 15-20 secs. if the engine is hot, there's no problem starting it.

Feel free to post your suggestions.

 

Coolant temp sensor maybe?

 

how can coolant temp sensor affect it?

 

Because it thinks the car is over heating so it goes to shut it down then it changes its mind.. eventually it will stall on you or at the least be hard to start sometimes .. hot, cold, idle, not .. no difference the problem is the sensor is getting a bad reading so the ecu thinks the car is operating out of normal temps and will shut it down or not allow it to start

 

No no... I had forgotten to put my oil filler cap back on. And when I discovered it and put it back on, the engine ran fine. I don't think the oil cap has anything to do with the idle if your idle is weird to begin with. But Yea, I thought about cleaning the IAC valve also, that may solve some idle problems because the valve can get gumed up. I've also heard that cololant temp sensor can effect idle speed too especially if it goes up and down. But for the stalling, I think cleaning the IAC valve can help.

 

so over 2 weeks you only drove 28 miles? Im jealous.

 

I drove my wife's car... my car sat. Believe me, I've driven it a lot. The car will be 5yr since I bought it brand new on August 1st and I have now 92,000 miles.

 

Ya know, my 97 max 5spd idles at like 500-525 all the time. It doesn't shake or anything and idles really super smooth.. I always thought it was low but I dunno.? Just thought I'd mention that.

 

I've had the same problem