[Mk2] [Turbo] Idle dropping to 400

[GT4kid]

Hi folks, my car has an idle issue. Car starts fine, does the cold start cycle then idles @ 900. After a blip of the throttle, it drops to about 400-500 then hunts its way back up. Sometimes stall at lights and roundabouts when easing off too.

Ive resistance checked the Throttle pos sensor, afm and isc valve. All are in range and terminals clean. looked for vacuum leaks but appear ok.
I noticed however if i unplugged the lambda it wouldnt do the hunting thing and idled at 1000 rpm consistently So i ordered one from tcb hoping it was the answer NOPE Still the same.

The afm has been modded 2 clicks but idle was fine in the past.
Ive removed the dump valve out the loop also to eliminate that.
This car is seriously getting my back up and after trawling the net for clues im still none the wiser. Hope someone can help[/quote]

[BenF]

Is this on a MR2 Turbo?

Does sound like a large air leak somewhere. You tried spraying WD40 over various bits of hosing / intake manifold to see if the revs pick up?

If that's no good, what's the compression like on the four cylinders?

[PW@Woodsport]

pull your fault codes first.

[GT4kid]

Thanks for the replies guys !! Forgot to mention i already checked for error codes, and nothing. I'll try the wd40 on the vacuum pipes this afternoon if the crap weather eases up.
Failing that , like you suggest, i'll test compression.

Anyone else had anything similar?

Thanks in advance for any further help

[benny p]

Sorry to hijack the post a little, but i am experiencing the exact same problem. From discussion with varous people it points towards a boost leak... as the car is making between 1 or 2 psi (it varies) below standard boost...

Anyway, with regards to the WD40, how does spraying on the boost pipes help? Do you mean the revs pick up and return to standard idle or isit that some WD40 seeps through into the engine and causes combustion that raises the revs?

Sorry if this seems dumb!

Ben

[BenF]

Sorry to hijack the post a little, but i am experiencing the exact same problem. From discussion with varous people it points towards a boost leak... as the car is making between 1 or 2 psi (it varies) below standard boost...

Anyway, with regards to the WD40, how does spraying on the boost pipes help? Do you mean the revs pick up and return to standard idle or isit that some WD40 seeps through into the engine and causes combustion that raises the revs?

Sorry if this seems dumb!

Ben

Basically the WD40 ( or any other lubricant aerosol ) usually is flammable. As the intake manifold is at vaccum at idle, if you spray on WD40 (or similar) to where the leak is it will suck in the WD40 along with air into the intake.

The lubricant then gets burnt and behaves like extra fuel and so the revs pick up very slightly. So when you're spraying around the area with the leak, if the lubricant is drawn into the engine the revs rise.

[benny p]

Thought as much! I'll give this a try! Cheers mate!

[Mike]

My car used to do this, I was gonna suggest the lambda sensor, but you've covered that already. How about the timing?

[GT4kid]

After checking all the vacuum lines and removing afm to turbo hoses and giving that the all clear ive done the compression test
Looks like bad news folks, after running upto temp, Ive just done the test and results are: cylinder no.1 150 psi no2. 130psi no.3 145 no.4 150psi .
As in the big green book, maximum difference no greater than 14 psi
I put a little oil in cylinder 2 and it rose to 150 psi, indicating ring or bore damage. Was kind of hoping it would be a sticky valve but NO GOD DAMN!!!
Does this sound like rebuild time or what??? This damn car is already a money pit, and my wifes gonna divorce me through it lol Im a slave to boost haha

Any advice on what to do would be greatly appreciated, or anyone with a Rev 1 or 2 engine going at a bargain let me know. Cheers

[BenF]

I wouldn't worry about being 5psi off ideal. There probably is a little wear there, but not enough IMO to warrant a rebuild unless you're burning a lot of oil.

I still think you've got a vaccum leak - maybe not the vaccum hoses, but perhaps intake manifold -> engine block ?

Do you have a boost gauge that you could plumb in to see what the vaccum is at idle?

[GT4kid]

Im glad you think its not enough to warrant a rebuild, i found it hard to believe as it only shows up on let off and once its done a bit of hunting it idles ok. Ive got a boost gauge fitted and and it reads between -20 and -15. on idle. Does this sound right? If this is the measure your referring to?
Thanks again for reply m8 !

[benny p]

hey man, as i said in my PM to you, i fixed my idle prob due to a boost leak..

In response to your q about psi reading, when my idle was funny after coming to a standstill and expecting the revs to fall the typical idle amount it would go to about -15psi at the lowest revs (circa400) and then creep to -20psi along with the revs creeping back to standard!

fingers crossed for a boost leak eh?

[GT4kid]

Hey folks, im pleased to announce i can put this thread to bed after months of head scratching and swearing.
Finally my idle problems cured.
I whipped off the throttle body at the weekend, took the idle control valve off and give it a good blast an soaking with carb cleaner, it was pretty choked up. Then gave all the little vacuum ports and inner channels in the throttle body a blast of compressed air and carb cleaner. Imparticularly, the little vacuum port next to the idle control valve inside the throttle body (from the rocker cover vac pipe) was completely blocked.
So after a damn good soaking and cleaning of the throttle body and resetting the tps sensor my cars bob on again yeee haaaaaaaa lol im so happy!!!!

Thanks for all the previous help, should of tried this weeks ago.

[BenF]

Cheers for posting back the solution - its good information for anyone in future.

Pleased to hear it is sorted