LEDAVE23

ok so hear it goes i have a 89 s5 vert, when i first got it it was running fine no issues ,except when it would warm up at idle the check engine light would come on but if i would rest my foot on the throttle without giving it gas it would go away,so i ran the code and it was a tps code,so i replaced it ($400 ) and i set it to specs with a multimeter and with the l.e.d trick ,and now its acting up i get a slow idle surge from 1,000 to 1,500 rpm when its cold and when its warmed up it would drive fine but when you put the clutch in or stop the idle would be rough and drop to about 500 to 600 rpm for about 5 to 10 seconds and then it will idle fine,so if you can please help its really annoying,what could have changed from just changing a bad tps for a new one oh yeah since i changed it no more check engine light just the idle issue

jjwalker

Redo the 2 LED setting method. When you get one LED lit and not both, turn the screw 1/4 of a turn higher. The blip the throttle linkage a few times to make sure it stays at 1 light on, one light off at the resting position.

The spring loaded adjustment screw is kind of cheezy, in that it can change after blipping the gas, but fortunately, after blipping the gas it wont change anymore. By the way, when you blip the throttle, don't push on the TPS side of the linkage. Either go hit the pedal or reach around to the other side to do it. I had the same problem as you and doing that worked perfectly.

LEDAVE23

i tried that and had no luck ,this is so frustrating

LEDAVE23

anyone else have an idea????

LEDAVE23

????

jjwalker

I'd check for a vacuum leak next. That is the second most common culprit in idle issues behind the TPS.

LEDAVE23

i went over all the vacuum lines like 100 times,im really stuck

monterx7

iTrader: (1)

i know vac line cracks can sometimes hide pretty good. i spray brake cleaner around suspected areas and see if the idle changes....

LEDAVE23

i did that too im positive its not a vacuum leak,is there any thing else that would need to be adjusted after the new tps ???

LEDAVE23

anyone else have a clue?????

LEDAVE23

wow 144 views and no one knows lol

calpatriot

On my 86 the FSM requires that you first adjust the idle speed and mixture before you can properly adjust the TPS.

There are at least threee ways of adjusting the TPS: the two light method, the voltage at the ECU method, and the resistance method. I have tried one and three, and have found excellent success with 3--adjusting the TPS for *exactly* 1000 ohms resistance at idle throttle.

Mine has a double throttle diaphram, I think yours does too; it is only active when the car is cold. Check for vacuum leaks around this diaphram and the hoses leading to it when the engine is cold.

That your engine does not idle well when warm suggests that the air-fuel mixture is off. You can check this by measuring the voltage coming from the oxygen sensor at idle. At idle the system is supposed to run a bit rich, which will show up as the voltage on the sensor at or greater than 0.5 volts. It should stay rich during acceleration, alternate between rich and lean at steady rpms, and go lean during decelleration. It sounds to me like it may be lean at idle.

The main method the ECU uses to control idle speed is the BAC valve. There is a check in the FSM which simply involves disconnecting the electrical connector to the BAC valve, and seeing that the rpm drops slightly. You might try that check to see if the variations stop as well.

I would check also the operation of the fast idle cam the double throttle diaphram and its delay valve; as well as timing and advance.

It really sounds like extra air is getting into your intake tract after the air flow meter. This could be a vacuum leak, or a malfunction in the air injection system (air control valve, port air valve & solenoid, split air valve and solenoid, and relief valve and solenoid.) All of these have pretty easy check procedurse in the FSM.