About a month or so ago I developed a high idle. It was also just had crappy driveability too. I did some exploring and found one of the plenum couplers was torn. I couldn't even pressurize past about 14-15 PSI as the air came out just as fast as it went in at that pressure. I ordered two new couplers and reinstalled. While I was in there I also replaced many hoses with silicone and ziptied or worm hose clamped everything. I had a machinist make me a plate to bolt in place of the TB so I could pressure test just the post TB section with the y pipe out of the way. I can now air up to 25 PSI and it holds great. I then hook the rest of the boost inlet system up and test from the IC inlets. Again, it holds great at 20-25 PSI.

Now on the road I am still getting the high idle (about 1150) with soft code stating the TB is at full stop suggesting there is still a post TB leak, but that whole system holds 25 PSI like a champ?!? I have also cleaned the TB and done the TB reset every time I clear codes.

Are there any check valves that could be killing me? Anything funky with using the 74mm TB that could cause this?

My #16 check valve is newish and I have checked for leaking past that.

Other than the high idle the car is driving great now.

Anybody have any ideas that I have not already explored?

Pertinent details: 74mm Tbody with IPD plenum, MAFless Cobb tune, Filters on turbos, Speedtech IC's, Forge boost hoses.

 

Are you saying the round cast part that the brass nipples are threaded into houses a check valve or are you referring to the check valve on the right side that goes towards the oil tank?

 

Another bit of info that may be relevent is it will only have high idle after then engine has fully warmed up to operating temp.

The last boost leak test I did was while everything was still warm.

 

I fixed this.

I replaced with check valve between the IPD plenum and oil tank. I don't think the issue was with the mechanical operation of the check valve, but the barbs on the yellow side. They had gone completely smooth. I'll bet the vacuum was leaking past there. It makes sense that this didn't show up in a boost leak test because the check valve was working. I did blow propane over that area as best I could with the engine running, though, but no change to idle quality.

I'm glad to have my car running right again.

 

Good call Steve !

 

congrats! good day for no longer hunting for idle hunting fixes. a new maf solved mine today too.

 

Glad you got yours figured out too.

 

thx, can you believe i went several months driving around with needing to turn on the a/c a stoplight so the car would idle normally? when all the while all i needed was to replace the maf in 30 seconds? i just never suspected it since i replaced it a couple of years ago.

so, anyone that says the cars don't "fry" mafs with 1.3 tunes and by *occasionally* bouncing of the rev limiter at 7200rpm is ill informed lol...and previously i thought only the cheap "knockoff" mafs got fried. oems do too.

you were wise to get a mafless tune. it happens again? i'm gonna show up at sam's door.

 

Thanks for the follow-up! I have a very similar setup, and same issue. I'll be checking those connections!

 

Go MAFless mark!!!

 

Glad to hear good news. There's a new valve being used on those in the last several years... if anyone needs help let me know how I can support you and IPD. They are great and have some cool products for us!

 

My high idle was cause by the vacuum line that goes to the FPR had come off at the plenum. A good one to get resolved for sure.

 

ha, so much to do, so little time.. plus if i went mafless.. it wouldn't have been something so simple as replacing the maf to cure the idle issue!

plus its one of the few things i can do myself other than breaking stuff

anyway, the car runs like it should. once again.

 

Nice!

 

Here's a shot of it.