RPM Idle 775-350-775rpm's (long)

[p5T]

Anyone's best guess while I'm here @ work?

I'll stop by autozone on the way home tonight and get the codes read.

There is no CEL though.
Used 1 can of carb cleaner and found no vac leaks.
pulled the crankcase breather and put my finger over it, no change.
hooked up my mity vac, pulsing showed 17-22hg.
pulsing goes away when AC kicks on to high.
Coolant Temp Sensor measured 965ohms and rose to 1005ohms 10 min later (means it's working)
cleaned maf
I replaced the bov with a straight pipe to eliminate possible source of leak.
I have a turbo w/ blow through maf set up.
also while datalogging w/ WBO2 my rpm's fall before a/f decreases and as the a/f decreases the vac hg increases from -25 to -21hg (af dithers from 14.4 to 17 or so.

Thought it was a leak between maf and TB, or vac leak...

car holds boost (only run 7psi) so I don't think its a leaking egr...
not sure when it started(maybe two weeks ago, ac is on a lot)

uses no antifreeze or oil but I haven' compression tested to rule out HG yet.
didn't know if anyone else knew or has run into this...

thanks, I am stumped...

 

[mopiko]

There's a TSB out for P5s regarding our ECM. Something about reprogramming the ECM to rid of rough idle problem. My experience was overrev on idle. My stock motor idles at 2,500rpm and they reprogramming it for me for free. Most of the other members here, however, have rough idling like you and got it fixed that way, maybe its worth a shot. Good luck.

 

[falsedawn]

I had an erratic idle due to the egr valve being carbon'ed up and stuck in the open position. Took it off, cleaned it in carb cleaner, reinstalled, and fine now.
It threw a CEL 50 miles after the problem first manifested itself.

 

[P-Funk!]

Swap the PCV valve. When there was no change plugging the breather - i think you found it...

Let me know.

 

[peepsalot]

I had an erratic idle due to the egr valve being carbon'ed up and stuck in the open position. Took it off, cleaned it in carb cleaner, reinstalled, and fine now.
It threw a CEL 50 miles after the problem first manifested itself.

Which CEL did it give you?

 

[peepsalot]

Swap the PCV valve. When there was no change plugging the breather - i think you found it...

Let me know.

What should happen when plugging the breather?

 

[P-Funk!]

idle should change...

(now maybe i wanna' go outside and check that...)

Could i be wrong?

 

[p5T]

I was wondering if our PCV valves could handle boost, it doesn't look any different then my miata one and that one has been boosted for 2 years(guess I could swap and find out)

 

[p5T]

There's a TSB out for P5s regarding our ECM. Something about reprogramming the ECM to rid of rough idle problem. My experience was overrev on idle. My stock motor idles at 2,500rpm and they reprogramming it for me for free. Most of the other members here, however, have rough idling like you and got it fixed that way, maybe its worth a shot. Good luck.

Thanks, I didn't know about the TSB.

 

[registering]

I took mine to Mazda for the same reason years ago, there was no TSB for it, and it was VERY bad. They said there was no problem, that's the nature of things. It was a very depressing intro to owning a Mazda, especially since I got rid of my Saturn for the EXACT SAME REASON, and bought the freakin' Mazda. The problem has faded over the years, now it happens once in a blue moon, and the car doesn't shudder like it's about to stall like it used to. I have never seen a 4-cylinder engine that idles well. I'm sure they exist, I've just never seen them (no not even my dad's Toyota!). Sadly I'm not impressed with the current state of automotive engineering when something as basic as letting your car sit there and idle doesn't even work properly.

Okay I'm done venting, I now return you to your regularly scheduled thread.

 

[mopiko]

Thanks, I didn't know about the TSB.

No problem, it doesn't mean it is definitely the ECM problem, but it doesn't hurt to try. It usually happen when the car is stopped at a light for some people I saw, for me the engine rev really high (2,500rpm) when I cold start but I don't have the rough idle problem like you. The engine, however, threw CEL several times during the cold season. Interestingly enough when the car is in the shop the CEL wasn't on but they were able to trace back, guess the comptuer would save the CEL code...

 

[falsedawn]

No idea what the code was, but this seems to be a common problem. p5T - is your car idling badly at all times, just when cold, just when hot? Did it happen suddenly?
You could try tapping the egr valve with the car running - if it's sticking, this might unstick it - if so, and it improves your idle, you know where the problem is.

 

[p5T]

Found it...

Moved MAF to BEFORE turbo and problem went away, moved MAF back to charge pipe and issue returned...
I know MAF's are sensitive to back turbulence, not sure what changed in 3 mos, will need further investigation.

 

[mopiko]

Glad that hear that, I hope the problem will stay away from your car forever.