I've got a 1989 745ti.

Back in the days when it was running (it's parked awaiting new turbo) I had some issues with what I believe to be the timing.

Here's the symptoms...

When I start the car, it idles rough. As the temp gets warmer, the idle smoothes out, but if I turn the car off, and turn it back on in like 2 minutes the idle is rough again.

Performance all throughout the RPM range is less than what my friends that have 700 series turbo's (1990 745ti, 1988 765ti) is.
Like if they floor it at operating temp from a stop, the throttle response is almost instant, and it snaps you back. Whereas with mine, the power builds slower. It's not as snappy or as direct feeling as my buddy's cars.

The power grows slowly, peaks at around 3000 rpm (at which point sometimes one of the back tires will light up), and then dies out until around 4500 rpm when it pretty much stops accellerating, and then the tranny shifts. 0-60 is probably 9 - 10 seconds.

So I went at it, replacing plugs, wires, cleaning throttle body, replacing all hoses (including all intercooler hoses and couplers), blah blah blah.

There's no black smoke, what little acceleration there is is not jerky, compression checks out fine, plugs are new, new FPR and fuel filter... I have yet to clean the injectors, but I wouldn't think this would affect power delivery only in low RPM and high RPM, but let the car get the good mid-rpm performance I'm seeing.

So, I'm thinking it's the timing. What do you guys think it is? I was thinking it was the turbo, but the turbo wouldn't cause poor low RPM performance, would it?

The car has 140k miles on it, FYI. Reason I'm re-doing the turbo is that it was only pushing 4.5 psi at full boost... and full boost was hit at about 2000 rpm, and held up to 4500, but power delivered at those RPM's was crappy except for 3000-3500...

Thanks

Ryan

Check knock sensor (KS) for around 5 M Ohms resistance. If you read K Ohms or infinite resistance, replace with a new KS.

Would the knock sensor cause odd performance maladies at different points in the RPM band, and simultaneously cause rough cold idle (but smooth as silk warm idle?)

Ryan

I'm wondering if you cat could be plugged, if you remove it and notice a huge diff then it's no good (the cat). The more i think about it the more I think it could cause your symtoms. Post your results and let us know.
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88 765 w/2stage boost & G-valve (TO.)

Ever try your o2 sensor? The car could be rich all the time without you knowing. Try installing an A/F gauge to see the mixture you're getting. I seem to have the same problem but haven't gotten around to checking it out yet. I will check out my cat soon though.