Rough idle while...

...a/c is on? Revs way down (almost turns off) and then revs up seconds later. Just Pulled and cleaned the throttle body and IAC valve? Going to replace the spark plugs next, then the fuel filter maybe?

 

I have a 2nd Gen, but do you only seem to notice this when it's cooler outside?

 

I wouldn’t throw parts at it unless you need/want those parts replaced for peace of mind.

Shotgunning parts usually just makes someone think it’s a big issue because they’ve done X, Y, and Z and it’s still broken because A was the problem the whole time, so a lot of time, money, and stress.

 

Yes I do, usually in the early mornings while the a/c isn’t even on. I think it’s a cold start issue.

 

I agree. I have an intake which was the primary reason why I started with the throttle body/IAC cleaning. I also cleaned my MAS.

 

I got to thinking about this and it just might be "normal" for your truck given the mileage. The IAC works because you say it revs up a few seconds later. Not being "right there" I can only speculate on a few things. I am thinking that the "base idle" is too low due to age of everything on the motor. Dont go and start tweeking the throttle stop screw to raise the base idle... there is a possibility that you can turn it so far that the TPS is now out of range. For an experiment disconnect the electrical connector that goes to the AC magnetic clutch and turn the AC on to see if the PCM sends the "Idle up" signal to the IAC and she speeds up. If she does not then there is an issue there but I doubt it.

I have seen where guys that have the test equipment will elongate the TPS holes/slots to allow for a greater rotation of the TPS and raise the base idle via the screw then adjust the TPS back to its "idle" settings. There is built in slop where the TPS indexes on the shaft and sometimes you get lucky. Of course all of the above is a "hack" and it takes time. My assumption is that the engine is just tired and she doesnt have the "omfp" she had when new.

 

Hmmm interesting. The truck on had 150k miles on it and runs great. Bought it with 100k on it. I installed an intake and exhaust. I’ve recently pulled and cleaned the throttle body and IAC. I plan to change the spark plug due to not knowing how long before the plugs were replaced before I purchased the truck...

 

Clean your mass airflow sensor, they get dirty over time with mileage and can cause wonky idling issues and stalling. Use MAF cleaner specifically, not generic electrical parts cleaner. It's easy and cheap to do

 

My 4 banger in my 2003 had similar issues before and after the rebuild... the throttle body was worn out and the throttle plate wouldn't sit in the same place every time. Check the PCV valve too... if it rattles it is good.

When you say you installed an intake and exhaust... what do you mean?

An 01 with only 150k on the odo? damn thats low mileage. My 03 had just under 400k when I had her rebuilt last year.

 

Did you pull the EFI fuse or negative on the battery after doing this?

idle should be constant no matter the age of the vehicle. changes mean it's not running in optimal condition and needs attention. slight variations are OK but swings are signs of an issue.

the rattle test is not always accurate. if you can vacuum test it that can tell. worst case just spend the $7 and replace it

 

I installed an after market intake and exhaust. Yea, it’s barely broken in at 150k haha. Will do Thanks.

 

Don’t think I’ve ever seen a 4 cyl engine not noticeably affected by ac. Or are you saying it’s constantly pulsing up and down while the ac is on? Most likely a vacuum leak. Happy hunting.

 

Yes. It will start up fine in the early Morning, I’ll drive somewhere. Goto turn it back on and it instantly dies. Also when the a/c is on it pulses and almost dies and then revs up. Weird.

 

I did not pull the fuse or disconnect the battery.

 

this will help the ECM re-learn the mapping. It should auto adjust but this forces it to quicker.

also it can take a few days or over 100 miles to level out

 

I’ve been driving it all week, is it too late to disconnect the battery?

 

it probably should have corrected itself by now but it never hurts to do this. it will (should) be high idle for a little while until it calibrates for the increased airflow.

as previously mentioned by @Glamisman when you clean the carbon deposits from the inside and around the butterfly valve it can leave gaps that affect the airflow at idle.

 

My 1st gen with the 2.7 does. Been wondering what causes it.

 

When it's cooler outside (65°F and below), the A/C compressor cycles. This is normal.

 

Good to know. I have no problems when the A/C is on. Or when it's hot outside. Just when it starts getting cold for winter and during the winter months.