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I'm having funky driveability problems - some knocking and lessened power at acceleration which happens seldom (couple of times a day). The problems are not too much annoying, but I want to fix them nevertheless.
I would appreciate all ideas, however crazy.
The car likes to have "diesel" sound (is it knocking?) at times, and the idle speed doesn't really stay constant. Unfortunately I have just changed the engine mounts, so the varying idle is not noticeable by listening for it; only the tachometer shows that revs sort of float between 550 and 800. Not too wildly, but nevertheless.
Here's the current status:
0. RPM sensor wire does have some cracked insulation, but the sensor itself seems to work fine. I have never seen any signs of it trying to fail (tachometer never "drops" nor anything).
1. The car starts perfectly every time, never had a problem with that.
2. Throttle body is cleaned (was full of oil crud), TPS readjusted, after about 4 months the TB is just as shiny clean as it was (plugged PCV was the culprit).
3. Cleaned the distributor cap - had some fuzz at the points, not too much, cleaned rotor too.
4. New plug wires (Bougicord) and spark plugs. Coil wire still original Bougicord, seems to be fine - no telltale signs of insulation going bad.
5. Verified all injectors are working by disconnecting each one and noticing idle stumble and subsequently recover. Used the self-test of the ECU as well - connecting one injector at a time and making sure it ticks. Also made sure not to mix up the injector wires (I labeled them permanently).
6. "Spray for leaks" seems OK - manifold gasket, TB gasket, vacuum lines, all that stuff -- both with water and WD40. No change.
7. 3 months after changing them, the plugs look fine - no signs of overly lean nor rich mixture.
8. The IAC valve is OK - it compensates when I obstruct the air flow by squeezing the hose tight.
9. Disconnecting the MAP sensor (manifold air pressure sensor) makes the car die at idle. I wonder whether the MAP sensor could be failing in a way that makes the idle rough and occasional diesel sound.
I've checked fuel pressure at the fuel rail at idle, got 30psi. Revving it up manually to about 2000RPM (by turning the cable pulley) gets it up to about 38psi. But, and I don't know how big a "but" is that, removing the vacuum line from the FPR doesn't seem to affect the idle at all. Only reinserting it makes the idle change for a second or so. The FPR definitely doesn't have a punctured membrane, and the fuel return line has ample flow in it.
The car used to display (once a month or so) check engine light with trouble codes (they would always be together) for lean/rich mixture at idle (conn. 2) and knock sensor signal faulty/absent (conn. 6). It didn't recur in the last 40 days (the last time I cleared the codes).
Since the TB was crudded up really bad due to clogged PCV (cleaned about 4 months ago), I assume that the tips of injectors may also have a lot of crud on them. I will pull the injectors with the whole rail out, look at their patterns, clean them, and compare spray pattern before/after cleaning.
Apart from that, I'm at loss what else could be wrong. I assume that dead O2 sensor would produce some codes, and that dead engine temp sensor would too, right?
Would knock sensor problems actually make the engine run lean / overly advanced and produce "diesel sound" (knocking)?
The car does 0-60 in perfect agreement with the manual (down to the precision of me starting and stopping the stopwatch).
Cheers, Kuba
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