Car won't rev past 2.5k, idles above 1k.
 

Hey guys. Fully built bottom end and supercharged here. Techs are stumped. Weird thing keeps happening where the car won't rev past 2.5k and it idles just above 1k. I looked around and saw one thread on it but it doesn't help. Any ideas? I have a 2010 manual G coupe. I replaced the ECU and the VVEL controller and the issue is still happening. ECU was an exact match (2010 manual coupe ecu).

Have you tried talking to your tuner about this issue? It seems like it is in limp mode.

I've run into this issue a couple times when I first started tuning the supercharger kit and when I went with Topgunz A-A setup. Goes into limp mode. The tuner should be solving this issue.

My tuner said to check the extension harnesses for the TBs and MAFs.

Ah, so you have the Stillen Supercharger setup.

Yeah I listed all mods in OP.

Yes!
My TB extension harness still gives me limp mode at random/unpredicable times and has for years now. Might be fine for 6 months then plays up 2 or 3 times in a shorter (days/weeks) succession.
I still don't believe there is a proper fix for this including replacing the ext harness with a newer (upgraded) one from Stillen. Very annoying and unsafe! :mad:

Limp mode is where the car has almost zero throttle. That's not the symptom I'm having. I'm having a symptom where the car idles above 1k and won't rev past 2.5k.

Limp mode is a general condition where the computer reduces power of the engine. There are various causes. You might see revs limited to 5K RPMs or 3K RPMs or less depending on the cause.

Right but it also makes the car rev super slow. That's not what I'm experiencing. My car revs at normal speed. It just caps at 2.5k and idles above 1k. In limp mode, the car revs really slow through every gear. That's not what I'm experiencing.

Not true. I've had limp mode hit me on the track due to oil temps and limit me to 5K RPMs. Other than the rev limit reduction, there was no perceptible change in throttle input or driveability. There are various levels of limp mode - you are referring to a more extreme condition. But still a version of limp mode.

Engine codes?

OK. :tup:

So I replaced the extension harness with a brand new one yesterday. So far so good. No issues at all. Drove the car for 10 minutes. Shop is going to drive the car for the next few days to make sure everything is good to go. Will post update if anything happens.

No codes at all.

So the tech just drove the car again. So far so good. He's gonna drive it a few more times after he cleans the MAFs and TBs. Should be good to go. This is my build list if anyone is interested....

2010 manual G coupe

CP Custom Forged Pistons with WPC Treatment
Carrillo Pro H-Beam Forged Connecting Rods with Upgraded Bolts and WPC Treatment
Walboro 520 fuel pump
CJM S1.SE Fuel System
ID 1300X CC Injectors
NGK Sparkplugs
Stillen Supercharger kit with Topgunz Air-to-Air Intercooler Setup and TIAL
Motordyne Longtube Headers
Motordyne Catback Exhaust
Setrab 34-row oil cooler
OS Giken Superlock Limited Slip Differential with GReddy Diff Cover and Whiteline Bushing
OS Giken TR Series Clutch
ZSpeed CSC Slave Cylinder Upgrade
EPS Oil Gallery Gaskets
EcuTek with Speed Density Tuning by Specialty-Z

https://cimg4.ibsrv.net/gimg/www.myg...8e657aee5c.jpg

https://cimg2.ibsrv.net/gimg/www.myg...871bf9d3dd.jpg

https://cimg3.ibsrv.net/gimg/www.myg...53cadc149c.jpg

https://cimg5.ibsrv.net/gimg/www.myg...08900ed4d1.jpg

https://cimg8.ibsrv.net/gimg/www.myg...8d1cb889bb.jpg

https://cimg4.ibsrv.net/gimg/www.myg...a9891857f5.jpg

https://cimg5.ibsrv.net/gimg/www.myg...67ada6b2b8.jpg

https://cimg0.ibsrv.net/gimg/www.myg...40db7679c8.jpg

https://cimg7.ibsrv.net/gimg/www.myg...ebd31d4a0f.jpg

https://cimg8.ibsrv.net/gimg/www.myg...2c95cc9fc7.jpg

https://cimg9.ibsrv.net/gimg/www.myg...6eb26cae1b.jpg

https://cimg7.ibsrv.net/gimg/www.myg...ceb34744bb.jpg

Bad news guys. Its still happening. Not sure what the deal is. Shop cant figure it out either.

Expect a P1239 when you least expect it if you're using a TB ext harness. This has been my experience.

Just a guess here but the extension may change the wiring enough that it is acting like an antenna and picking up noise from the other electrical systems. I'd try shielding the harness* - but that may be more work than it's worth.


*Edit: As much of the TB wiring as you can, not just the extension.

Still happening. Shops can't figure out what it is. May have to take it to the tuner (Specialty-Z) to have him figure it out.

And mine threw another P1239 again, the day before yesterday! :mad:

I think people have done this and it still isn't 100% reliable.

Replaced the TBs. Still having the problem. Gonna have to take it to Specialty-Z to figure out what it is.

Replacing the TB's has never fixed this problem form what I've found out.

My car is completely stock, and i've experienced a similar issue. car runs perfectly fine 99% of the time. at random the idle will jump to 1k rpms, it will accelerate (past 2.5k rpms) but feels like it has 10% of its normal power. After a restart it will typically be fine. I have brand new MAF's, and new MAF harnesses with perfect continuity to the ecu. No CEL's ever, and doing datalogs i can't see where any readings change to the point that it would cause an issue. I suspect the MAP sensor in the IM may be going bad, but im not sure if the ECU references MAP or MAF until closed loop... I'm interested to see what you find

Things that I replaced:

The ECU
The TB Harness Extension
The TBs

None of the above has fixed the problem. We will see what Specialty-Z says.

Any update?

It s clear a lot of people don't understand how to troubleshoot complex problems. A diagnostic tool in live mode should reveal plenty information to aid solving this problem.