Rough running

[sloweddi]

Howdy,
I have a 1989 accord LX-I. It has been a great running car. Recently, when the car has warmed up, it will start running rough. the tach will jump from a good idle (about 800) to 3k. The engine will correspond with a momentary surge up and down matching the tach. I have noticed that sometimes when I am stopped at a light and I take my foot of the brake pedal, the rpm drops down to normal but then goes back to the up and down surging (?). Recently the "battery" light has come on momentarily when the rpm drops down to the idle range. And just to screw with me, sometimes the car will run perfect.
I have done a yearly maintenance and replaced the plugs, wires, PCV valve, air filter, distributor cap, and cleaned the IAC. This has caused no change in any of the symptoms.
I checked the ECU and there was no blinking lights. I tested the alternator by placing my voltmeter on the battery and got an idle voltage (after warmup) of 14.28V. The voltage did not change as the engine ran rough.

Any thoughts??
Thanks

[Demon1024]

A failing alt will cause these cars to do some crazy things. Make sure your grounds are in good condition, or even add some more! Usually the tach jump means it's gonna fail, but a weak ground/ alt can cause it too. It's sounds like you may want to look for a vacuum leak too. I'd start with the fast idle valve. Try screwing it down and see if that doesnt fix ya up. You can adjust it properly when the car is cold starting up and moving it up or down to an appropriate cold idle speed. It's kinda tricky unless you have a 3" wide screw driver. I've used 2 flat heads or butter knives to do it. Just don't strip the top out

[Oldblueaccord]

I would not move the fast idle valve unless your COLD idle is to high or to low.

I would check that the throttle body is returtning fully . Pull back on the gas pedal if you have too.

Also how is your gas mileage has it gotten real bad lately.



Wp