1991 TPS issues, idle issues.
Thread Starter
7th Gear
Joined: Feb 2025
Posts: 7
Likes: 0
1991 TPS issues, idle issues.
Hi everyone,
After recently changing out an IAC and resetting my minimum idle, it seems that now my TPS does not want to agree with where I set the min idle screw.
When I go thru the min idle setting procedure (Diagnostic mode, unplug IAC, start car warmed up w/ nothing on, and set idle to ~450 rpm in park) my TPS always reads quite high being around 0.73V from ground to the signal wire. For my TPS to read correct (0.54V) I would need to back the min idle screw almost completely out which in turn makes it to where the car will not even start with the IAC unplugged.
Does this mean my TPS is bad or should I set the min idle screw to where the TPS reads .54? The 5V reference wire is acting as normal and on these cars, the TPS is not adjustable so I have to assume that it is just working incorrectly. Also it is worth noting that my idle has been quite rough during testing though the car doesn't report running particularly lean or rich and the car has no vacuum leaks or anything of the sort.
Any help would be greatly appreciated.
Thanks.
After recently changing out an IAC and resetting my minimum idle, it seems that now my TPS does not want to agree with where I set the min idle screw.
When I go thru the min idle setting procedure (Diagnostic mode, unplug IAC, start car warmed up w/ nothing on, and set idle to ~450 rpm in park) my TPS always reads quite high being around 0.73V from ground to the signal wire. For my TPS to read correct (0.54V) I would need to back the min idle screw almost completely out which in turn makes it to where the car will not even start with the IAC unplugged.
Does this mean my TPS is bad or should I set the min idle screw to where the TPS reads .54? The 5V reference wire is acting as normal and on these cars, the TPS is not adjustable so I have to assume that it is just working incorrectly. Also it is worth noting that my idle has been quite rough during testing though the car doesn't report running particularly lean or rich and the car has no vacuum leaks or anything of the sort.
Any help would be greatly appreciated.
Thanks.
Melting Slicks
Joined: Aug 2011
Posts: 2,844
Likes: 176
Speed density with 20-25 iac steps is normal to have a range of .67-.76 vdc. At start up the ecm sees this voltage and recognizes it a zero % throttle. Tpi maf 85-89 tps is .54 vdc. You can use a adjustable tps on speed density from 85-89 not sure why but it’s often cheaper than non elongated hole 90-92 Tpi tps.
