Just out of curiosity, does the engine's idle wander around? I'm still suspecting that when the head was milled, it affected the timing chain function enough, so that the tensioner range was no longer effective. I've seen this before on old BMWs. When this happened there was a company that made quality thicker head gaskets to take up the slack. But, that was when engines had 9.3:1 compression. Not 11:1 and run to +8K RPMs.

 

The idle is usually steady around the 900-1000rpm mark. We played with the idea of the timing chain and the TCT being the culprit. We replaced it all with no effect. A thicker head gasket has been discussed and may be my next step.

 

Did you check the TPS? They can go bad. When they do they can play havoc on the ignition timing, and the car will run erratic and like poo in closed loop. Verify engine is at full warm up with no accessory's is idling at 4-5 degrees advance and your getting proper voltage at TPS at 0 to 100% throttle opening. Should be very close to 0.5v idle to 4.5v 100% throttle.

Lets not start yanking heads yet. Id be surprised if it was a mechanical issue - assuming you have already verified proper valve adjustment spec.

 

Great idea! I'll hook up car and try that out.

 

TPS shows 7% at idle and 90.5% at full throttle on the computer.

Other things to note:
The engine load shows 30% at idle
Long FT1 sits at -7% at idle and stays there at all throttle positions and revs.
Short FT1 starts at -7% and runs deeper into the negatives as the car revs.

Maybe it's a vacuum leak that I'm missing?

 

A bad tps can work ok ateach end of its range, but get flakey in the middle where it spends almost all of its time.

I don't know if our tps is a wipe style potentiometer. If it is, when worn it can get very erratic intermittently. This can be seen on a voltmeter by carefully watching the display as you sweep the throttle plate through its range. Instead of seeing the voltage steadily and uniformly rise in proportion to throttle motion, it'll start bouncing all around.

Don't just test a tps at both ends of its range.

A vacuum leak typically goes away at higher throttle, as the leak becomes smaller and smaller in proportion to metered air through the tb. At idle, the unmetered leaked air is high compared to metered tb air. So it can cause rough, inconsistent idle.

 

The TPS shows a smooth graph from closed to open.

 

Update:

Re-installed the injectors after they were flow tested. The testing may have clean them up because the car runs significantly better. The report showed no cleaning necessary and flows all within spec.. Bottom-end bogging issues and drop in power above 7k RPM has moved to 8k RPM.

The IAT shows intake temps are getting up to 170+ in traffic. It's 130-140 on the highway. Hopefully the new intake gets here soon to help that issue.

I have noticed that the short-term fuel trim sets to exactly zero under full throttle application. I don't know if that's normal. Someone smarter than me can chime in.

 

I've always considered intake air temperature would be maybe 10° (ten degrees) higher than ambient temperature on the road in the summer. Is that an accurate assumption? Even 130°F seems astounding.

-- Chuck

 

The stock location of the IAT sensor is on the back side of the intake manifold and that manifold gets HOT! I can't touch it with my bear hand even an hour later since I shut the car off. It's reading the hottest air temp point that the engine can take in. If it was closer to the filter, it would read cooler. I could relocate it there to read a cooler temp to trick the car, but that looks like a real PITA. The intake that the car currently has is about 6in from the header. It's a junk eBay intake that came with the car. It doesn't even mount to anything. It's just flopping around in the engine bay. That seems far from ideal.