OK, here goes. 90 FC3C, vert, 150 thou miles, great compression, new filters all around, fluids also, timing adjusted, new plugs, wires , etc, complete "OWNER" tune up, new AFM. Checked AWS, BAC, ok, new O-2 sensor, ready to put new TPS in and one question before I do. Why is it that when the car is cold, or warmed up, when I shift into gear at stopped position, is the rpm's erratic? Doesn't stall, just varies from say 550 to 1400 . Out of gear, idle is almost dead nuts, and doesnt vary. Putting in new TPS cause error codes came up 12 & 18 and when I checked it , its just over acceptable limits on high side. Any ideas, will new TPS fix this? Thanks, the Dog.

 

TPS bad or out of adjustment
TB throttle stop screw not adjusted correctly.
Dirty or cruddy TB that prevents proper closing of the TB plates.

Here's what's causing the cycling...
The engine wants to rev (for whatever reason).
There is a decel cut function for fuel which will cut the fuel injectors off at around 1,700RPM or so, when TPS = 0 - i.e. foot of the gas pedal.
Engine revs up...hits decel fuel cut...engine revs down...BAC valve cuts in to save idle...engine revs up again...hits decel fuel cut...engine revs down...you get the picture.

Usually the TPS just needs and adjustment.
I adjust the narrow range side to 1.0-kohm of resistance, with the engine full warmed up and TPS unplugged.
This will guarantee the TPS is within spec for idle.


-Ted

 

Gotcha, I have adjusted the "old" TPS to 1.0 , warmed up and unplugged, but getting reading of 6.12 at WOT. Got another TPS I'm ready to install, and have cleaned TB, I guess the best thing is to try new TPS, adjust everything, and see what happens. Also, I keep reading about BAC having to do with this also, but when I checked it out, 11.6 and battery check OK, so TPS is first and will advise on results. Thanks, any advice on simple adjstments I need to do after TPS installed?

 

I got a vert with 157K and I have the same issue, ie, idle fluctuates when engaged in gear. My problem was the condensor wire is loose (single black wire with little black box attached to the clutch slave cylinder). When I get it tight it runs right, but when it loosens it fluctuates. My problem is the hole is stripped and I can only keep it tight for so long. I couldn't get in there and re-thread the hole, so I guess I'll try JB weld.

 

that will have nothing what so ever to do with the idle, and only is a capacitor for the oil pressure gauge.