six35

I recently installed a new throttle position switch on my 91 c2. now the car idles high (about 1100rpm) and when i let off the gas pedal completely or get back on the gas pedal, the car hops kind of rough. so i figured that i need to adjust the TPS on the left side of the throttle body. is there any way this can be done precisely?

JasonAndreas

There are two places to adjust the throttle cable but one is a PITA to get to, the other is located behind your accelerator pedal. On the end of your throttle cable on the pedal end there is a threaded metal cylinder and a nut. To adjust the cable tension/travel you loosen the nut, turn the cylinder (RTLL) and then retighten the nut. When you loosen the nut make sure that you don't let the cylinder untwist itself or you'll have to turn it a thousand times to retension the cable. To get a better idea of what your dealing with you might want to pull the accelerator pedal off the pedal assembly. The other location for adjusting the throttle cable is in the transmission tunnel.

six35

well i thought that the thorttle was fine, because before i switched the TPS, the idle was perfect, so i thought that the problem i am having would come from the TPS not being properly adjusted!

Geoffrey

You can backprobe the connector and determine the idle voltage and WOT voltage. Specs are in Adrian's book. You adjust by rotating the assembly on the shaft by loosening the 2 philips head screws. No special tools other than a volt meter.

I doubt it is the TPS unless it is so far out that it is using the main fuel table (AFM Based)instead of the idle fuel table (TPS activated). Check for any intake leaks.

DaveK

This sounds a little confusing.

Unless I've just learned something new - there is no TPS on the 964, there is an Idle microswitch and a Wide Open Throttle microswitch.

I assume we're talking about the idle microswitch - but I don't understand the comment about it being "so far out". It's a microswitch - if it engages it will activate whatever is supposed to happen at idle, and if it doesn't - then it won't.

And if it doesn't - it will certainly screw your idle up.

JasonAndreas

The tiptronic based 964s use a throttle position potentiometer and the 5-speed uses a throttle position switch. The push-rod behind the accelerator pedal is also different.

DaveK

Cool - I did just learn something!

Lorenfb

"The tiptronic based 964s use a throttle position potentiometer and the 5-speed uses a throttle position switch. The push-rod behind the accelerator pedal is also different."

The 964 DME wasn't design for a TPS as was the Tiptronic unit. The standard Idle & WOT inputs are
52 & 53 respectively. The TPS is an analog input, as opposed to 52 & 53 which were designed for
0/5 volt levels. Although the TPS appears on Sheet 5 of the DME schematic, the TPS actually just
goes to the Tiptronic Unit only.

six35

alright, as soon as i have time, i will start by loosening the philips screw and using a multimeter to adjust everything.

thanks guys