OK, this will be long winded and needs some explanation.
I finally got around to driving my 86 on a regular basis a few weeks ago, and the first problem I noticed was: after commuting to work (or anywhere), and pulling into a parking spot, shifting into neutral or park, the engine wanted to idle at 1200 rpm. Strange, I looked at Direct Scan and my commanded idle was 850 but the IAC's were hovering in the 50-60 range
Even though the tps said .42 in idle (the reason I mention tps will become evident later).
When first starting the car and getting it warmed up (to test/set IAC and TPS) all is normal with idle rpm (850), IAC (10), and TPS (.42). But after driving around, the idle refused to come back down below 1200 and the IAC's were in the 50's again. I couldn't figure that one out at all, even the P/N flag was being set properly, so the PCM knew I was shifting into Park. It didn't seem to be too big of a problem so I decided to consider my other problem with higher priority.
While making the commute to and from work (about 9 miles each way) all two lane highway miles, so the car's speed seldom gets much over 58-62mph. Lately I started noticing the torque converter unlocking and re-locking within 1-2 seconds, sometimes 3-4 seconds.
And as any of you that have a vigillanty torque converter know, when it unlocks and locks back up, YOU FEEL IT! It was annoying even though it only happened 3-6 times per trip.
I started paying close attention to Scanmaster during these drives, and since it only occured at extremely light throttle settings, I switched scanmaster to the tps mode and watched as best I could. Even with the fast update code it still wasn't showing me anything out of the ordinary. Then it got lucky and caught one of the occurances. When the TPS was down in the .60-.80 range (just about where you're trying to let up from a light cruise), the tcc ulocked, and low-and-behold I saw scanmaster's tps display go to .22
What the heck??
I saw this occur a few more times over the next few trips and decided it's time to try and capture the event with Direct Scan. That's the beauty of DS with it's buffer, you can start recording after an event, and it's still captured!!!!!!!!!!!!!!!!
Sure enough, there was that hole in the tps voltage, dropping into the .2 area. This is far below the tps threshold to unlock the tcc in the chip so that's why it was happening.
So's I run down and buy a new TPS, get it all set and take the car to work today. Eureka!!! no more TCC ulock/lock problem. Must have been some kind of funky internal short to ground starting to develop that would pull the output voltage so far down.
An added benefit (that I haven't figured out yet), my idle now comes back down to normal when parking the car!!!! I still haven't figured out why it was causing that problem since when in idle position the TPS was sitting rock steady at .42 ???? but it was keeping the IAC numbers way to high???? Now, when shifting into park my IAC numbers come back down to 10 where I like them,
All's well
I finally got around to driving my 86 on a regular basis a few weeks ago, and the first problem I noticed was: after commuting to work (or anywhere), and pulling into a parking spot, shifting into neutral or park, the engine wanted to idle at 1200 rpm. Strange, I looked at Direct Scan and my commanded idle was 850 but the IAC's were hovering in the 50-60 range
Even though the tps said .42 in idle (the reason I mention tps will become evident later).
When first starting the car and getting it warmed up (to test/set IAC and TPS) all is normal with idle rpm (850), IAC (10), and TPS (.42). But after driving around, the idle refused to come back down below 1200 and the IAC's were in the 50's again. I couldn't figure that one out at all, even the P/N flag was being set properly, so the PCM knew I was shifting into Park. It didn't seem to be too big of a problem so I decided to consider my other problem with higher priority.
While making the commute to and from work (about 9 miles each way) all two lane highway miles, so the car's speed seldom gets much over 58-62mph. Lately I started noticing the torque converter unlocking and re-locking within 1-2 seconds, sometimes 3-4 seconds.
And as any of you that have a vigillanty torque converter know, when it unlocks and locks back up, YOU FEEL IT! It was annoying even though it only happened 3-6 times per trip.
I started paying close attention to Scanmaster during these drives, and since it only occured at extremely light throttle settings, I switched scanmaster to the tps mode and watched as best I could. Even with the fast update code it still wasn't showing me anything out of the ordinary. Then it got lucky and caught one of the occurances. When the TPS was down in the .60-.80 range (just about where you're trying to let up from a light cruise), the tcc ulocked, and low-and-behold I saw scanmaster's tps display go to .22
What the heck??
I saw this occur a few more times over the next few trips and decided it's time to try and capture the event with Direct Scan. That's the beauty of DS with it's buffer, you can start recording after an event, and it's still captured!!!!!!!!!!!!!!!!
Sure enough, there was that hole in the tps voltage, dropping into the .2 area. This is far below the tps threshold to unlock the tcc in the chip so that's why it was happening.
So's I run down and buy a new TPS, get it all set and take the car to work today. Eureka!!! no more TCC ulock/lock problem. Must have been some kind of funky internal short to ground starting to develop that would pull the output voltage so far down.
An added benefit (that I haven't figured out yet), my idle now comes back down to normal when parking the car!!!! I still haven't figured out why it was causing that problem since when in idle position the TPS was sitting rock steady at .42 ???? but it was keeping the IAC numbers way to high???? Now, when shifting into park my IAC numbers come back down to 10 where I like them,
All's well
