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Thought I'd hit you guys with this one.
So I put a 90 motor in this 87 745t m46 car I got awhile ago, it had a toasted thrust bearing. My 90 motor got rod bearings, epoxy on the oil pump pickup tube, ALL new gaskets and seals with the exception of the headgasket. All hoses and belts, radiator, reman distributor, all tune-up parts, injectors cleaned by me with new seals, TB clean, etc, etc, etc. Has a non-rotting Volvo engine harness and pretty new clutch. I did my homework.
Been on the road about 6K miles now, MPG is 26 or so, runs pretty good, been reliable. It has piston slap, but that isn't unusual really and it's less the warmer it is. The recurring problem is a slightly ruff idle and occasional quiet pop of misfire audible in the tailpipe and felt in the car as a slight shudder at idle.
Last time I pulled the plugs they were a little on the white side but not extremely so. I have checked extensively for vacuum leaks and found none. I covered all this pretty meticulously when I installed the motor. The AMM to turbo hose is new, plugs and wires new, distributor a Bosch reman, timing I've had at both 12 and 14, car feels a little better at 14 and never heard it ping other than once I got some crappy gas. Always run Premium. I adjusted and re-checked the valves before motor was in and about 1K miles after it was on the road. The valve stem seals were replaced, never seen the motor smoke. The ECU temp sensor is new also. It starts readily hot or cold, has decent power for what it is I think, pulls alright and holds boost till redline. Fuel pump is quiet.
I decided to check the mixture adjustment and with a meter on the o2 wire found it steady when hot at .8v, and the LED in the test port was lit solid, so rich mixture. Pulling a vacuum line would make the LED go off, lean, and the meter would go to low voltage, .1 or .2. Also, chopping throttle after holding 2500rpm or so would have it go lean till it reached idle, this is normal as well I believe.
So I got the cap off the AMM and put a meter on the line reading the voltage that is adjustable, started at 1.66v. When I got it to 0.24v I finally had the meter on the 02 oscillating more or less evenly and the LED going on and off at idle. I did observe the meter on the 02 was what I'd call hanging at either rich or lean every couple of sweeps, just for a second or so, then it would return to oscillating. It also oscillated at steady 2500rpm, but the LED remained lit. So in theory I made an improvement in things, and it runs OK. I still think the AMM needs to be replaced due to a flat spot at 2500rpm when cold.
BUT, my idle still sucks, still that little shimmyness. And it's only when hot, so presumably only when in closed loop.
I have checked other things I can't think of off hand, and some I might should but have inferred from other observations and not checked. I haven't done a compression check, but with no smoke, little oil usage, good cold or hot starts, good power, good MPG, I can't imagine compression is a problem. I haven't checked fuel pressure, but there is nothing in the performance of sound of the car to make me think fuel pressure, and it evidently isn't running lean, so.
The dash mounted vacuum/boost gauge is steady and about where I'd expect it to be when not in boost, so I haven't hooked a vacuum gauge to it.
So, I'm about out of thoughts. Injectors? I cleaned them carefully, though that may not mean much. AMM? Plan on replacing it as a maintenance item anyway. ECU? I despise throwing parts at a problem, but I'm running out of things I can readily test, and frankly I'm more than a little dissatisfied with the amount of work and money I've put into this thing and the way it still runs.
The car is very worth fixing, it's been painted and while not perfect at all is still shiny black, it's a stick, has the cloth/leather seats which I like a lot, there is zero rust or accident damage, and it's just generally a really sharp looking car.
Opinions?
Thanks..
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