89 4-cyl; no power at low RPM

First off, I don't know this specific engine.

In general, I would try to look at ignition advance at part throttle. Does the distributor have a vacuum can on the side? That would normally give you an initial kick in the advance just as you begin pushing on the gas pedal, so the engine would accelerate from idle. It also allows higher ignition advance at cruising speeds, with small throttle openings. If the diaphragm inside the can is leaking, or if the hose connected to it has a leak somewhere, it won't give you that extra advance and the engine won't respond well to throttle.

Also make sure all moving parts inside the distributor body are clean and lubricated, and move well without binding. This goes for the centrifugal weight mechanism parts too. If those are binding, the engine won't see enough ignition advance.

To verify either the vacuum advance or the centrifugal advance operation, use a strobe light timing gun and observe the timing changes when the engine is running. Repeated very small throttle openings should result in instant ignition jumps (vacuum advance). The centrifugal advance operation can be checked with the vacuum hose disconnected and plugged. If you get no change in timing regardless of engine rpm, then the centrifugal mechanism is not working.

You can also try to suck on the vacuum can hose to try to detect leaks. You should be able to suck a vacuum in the hose, and block the hose opening with your tongue... it should stay stuck to the hose, meaning the vac unit is able to maintain vacuum with zero leaks. You can also buy an inexpensive manual vac pump from most auto parts stores, if you don't like getting your mouth dirty :)

Another problem may be incorrect mixture. Troubleshooting and fixing this may get a bit more complicated and vehicle specific, so I won't get into that here.

Jan

Like Jan, I don't know the 4 cyl engine that well. Everytime I fill up, I thiink your friend has the right idea - he / she gets the Mustang experience with a little less bite at the pump. :-) Anyway, on the 8 cylinder, I'd look at the idle air control, if present on that motor, and possibly the TPS. I heard both suspected in low idle driveability concerns, although Jan's vacuum ideas are at least as good. The IAC gets gummed up over time, and is an expensive piece to replace, but 20 mins with a can of carb / throttle cleaner has NEVER failed me.

Jan Andersson wrote in news:66fa87F2kbrhjU1 @mid.individual.net:

It's an '89. All it's controls are going to be electronic.

I am going to help my friend tomorrow, we have two different service manuals and hope to check out sensors and find one that may be at fault. The spark advance is controlled by a TFI electronic control (I replied initially to this posting that fact, but it never showed up), and I've read that it can have problems with heat. I plan to try quick cool, etc to isolate. What my friend has told me is that the car does run fine for about 5 minutes when cold. Fine, but why would problems with TFI getting hot, be apparent only at low RPM, what would be the symptoms be for a heat failing TFI - no spark advance at all-? How would it work fine at higher RPM and not low RPM if TFI is failing? It would seem to me that something is giving the computer control module band info at for low RPM and I will be checking the TPS for one. Any other suggestions, opinions is appreciated.

Thanks

When the TFI overheated on my '89 four-banger, it would usually just suddenly and instantly shut the car down. More often, it would not allow a restart of a warmed-up engine, until it had had a half hour or so to cool down. This doesn't sound like your problem.

I would take Jim C's approach and start first by cleaning the air intake passages. The MAF sensor and idle air bypass are both easy enough to clean out (probably a LOT of gunk in that IAB, if it's never been touched).

See