Difficult to Diagnose Driveability issue

[djur]

1989 2.9L Ranger. Engine revs between shifts, a slow rev 500-1000 in gain before slowly returning. Intermittent problem (but frequent, every 10 mile trip it happens), seems worse when engine is driven cold. Problem can sometimes be cured by cycling ignition off and on while driving. TPS was recently replaced to try to cure a rough idle, replaced with aftermarket part from NAPA. IAC valve was replaced to try and cure an AC issue where the engine stumbles, and recovers continuously at idle, but only with AC on. This too was an aftermarket part, and one bought on the internet as well. Both parts I suspect could be bad (shame on me for buying aftermarket).

The TPS reads out 1.01 volts at idle and when revved (not sure how high, maybe 2000 RPM), it read 1.25 volts. I'm not sure how to test the IAC motor, I hear resistance testing is spotty, and I don't even know the values to look for. I touched an ohm meter to both prongs on the motor and got a 0.00 value, but I can't remember what scale I was using.

I cleaned the throttle body with throttle body and carb cleaner. I noticed of the two ports that go to the valve covers one had strong vacuum and the other none at all, I don't know the significance of this, but I'm curious if anyone knows the purpose of those ports.

I read codes out, both KOEO And KOER, both returned code 11 - System Ok.
I sprayed that throttle body cleaner on the vacuum lines in the engine compartment, but I think it was a waste since the engine did nothing but choke on the stuff while I was cleaning the throttle body, guess they do that to prevent engine damage due to too much highly flammable materials entering the engine. I hear brake cleaner works good for finding vacuum leaks... I haven't been able to find any any other way.

Any suggestions or ideas are helpful. I'm almost to the point of taking it to a shop, but I'm just worried no one there can find this problem without throwing parts at this thing.

 

[BIGHVM]

run it and spray wd 40 onto the intake manifold, if the idle changes when wrm you have an induction leak.
Do this only after clearing memory by unhooking battery for around 20 mins mate, hope this helps.

 

[djur]

So disconnect the negative battery cable for 20 minutes, warm the engine, and spray down any potential leaks on the intake manifold with WD40, and the flammability will cause the idle to change?

Did I get that right?

 

[wood1]

Don't spray it on the coil pack or plug wires, if you have a bad wire you'll find out really fast...

 

[djur]

I disconnected the battery cable for 20 minutes once the engine was warm, hooked it back up, started, and doused the intake manifold in wd-40... No results...

I then decided to clean things up a bit more, took the IAC off, the intake hose, blasted down the IAC, the IAC ports (both in front of the throttle plate and at the IAC), and scrubbed everything down with an old toothbrush. I then hooked everything back up, and tightened down the IAC nice and tight.

For some reason the symptoms have mostly disappeared, the problem only surfaces now when I run the engine very hard... If I get the engine to 4000 RPM in rough acceleration, it will try to idle up between shifts, and at the next stoplight, but the problem soon disappears, and the engine holds back like normal.

The odd thing is there are numerous other posts similar to mine, all of which seem to end in no resolution... I'm definitely not the first ranger driver who has had a ranger that revs or surges between shifts. I even find posts to this problem being RPM specific.

I found one post where someone was making reference to a resistor near the spout connector, anyone know the purpose of that particular device?