Problem with 85
Thread Starter
Cruising
Joined: Jan 2006
Posts: 10
Likes: 0
Problem with 85
I can't find an answer on the 85. I start it one time and it says service engine soon. I turn it off and restart and it doesn't say anything. This will go for a number of starts and then out of the sky it will say service engine again. The other problem is it will stall at a red light. This only happens every so often. It works for days and then I pull up to a red light and the RPMs drop to 500 or below and it stalls. It starts right back up. I have had the fuel filter and pump replaced along with the o2 sensor and a full tune up. The computers show nothing. Any ideas?
Pro
Joined: Feb 2009
Posts: 589
Likes: 1
From: PA
Maybe you have to reset the TPS (throttle position sensor). I think that's what it's called. It's on the right hand side of your throttle body (passenger side). Loosen the 2 screws and turn this black box left and right. You'll hear the idle change. This might get it from not stalling.
The proper way to adjust this is with a multimeter. I forget what the voltage should read on the meter for the proper adjustment. Someone else will come in here and tell you better than I did.
When I bought my 85 I had the same troubles. Everything was solved when I bought my GM 1985 Corvette Factory Shop Manual.
The proper way to adjust this is with a multimeter. I forget what the voltage should read on the meter for the proper adjustment. Someone else will come in here and tell you better than I did.
When I bought my 85 I had the same troubles. Everything was solved when I bought my GM 1985 Corvette Factory Shop Manual.
Melting Slicks
Joined: Jun 2009
Posts: 2,910
Likes: 10
From: Jesuit Bend Louisiana
Maybe you have to reset the TPS (throttle position sensor). I think that's what it's called. It's on the right hand side of your throttle body (passenger side). Loosen the 2 screws and turn this black box left and right. You'll hear the idle change. This might get it from not stalling.
The proper way to adjust this is with a multimeter. I forget what the voltage should read on the meter for the proper adjustment. Someone else will come in here and tell you better than I did.
When I bought my 85 I had the same troubles. Everything was solved when I bought my GM 1985 Corvette Factory Shop Manual.
The proper way to adjust this is with a multimeter. I forget what the voltage should read on the meter for the proper adjustment. Someone else will come in here and tell you better than I did.
When I bought my 85 I had the same troubles. Everything was solved when I bought my GM 1985 Corvette Factory Shop Manual.
Advanced
Joined: Jun 2006
Posts: 51
Likes: 0
From: Maryland
the throttle position sensor voltage and/or the IAC valve being dirty might be the cause of your stalling, Ask me how I know. The voltage measured on the top two vertically oriented wires on the TPS should read .54 +/- .08 volts at idle. If it is incorrect, you can adjust it by loosening the mount screws and adjusting accordingly while looking at your multimeter. Let me know if you need additional help.
Last edited by hmmorillo; Sep 16, 2009 at 07:08 PM. Reason: additional info
Pro
Joined: Jun 2001
Posts: 520
Likes: 6
From: Elverson PA
Look in the "old tech tips" at the top of this forum. There is a very specific procedure to set the tps and idle on these cars. The procedure detailed is for the 85. I would also take off the throttle body, take it apart and clean it while you are at it. If you search around you will find lots of info on how to do this. Sorry, I usually try to help more, but I have to go to bed.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
check for codes. first, disconnect the battery, drive it till the check engine light comes on, then interrogate the computer. That will tell you what the computer sees as a problem.
Fix that, and then if it continues, fuel, air, spark, compression...........engines don't run without them.
Find out which ones you have, and go after the ones you don't have.
Fix that, and then if it continues, fuel, air, spark, compression...........engines don't run without them.
Find out which ones you have, and go after the ones you don't have.
Pro
Joined: Feb 2009
Posts: 589
Likes: 1
From: PA
When this happened to me when I bought my 85 I didn't have a check engine light lighting up on the dash. The check engine light did and does still work on start up. I also wondered why it didn't light up at the time. Drove me crazy for a while, bad idle and no light. The GM shop manual showed me the way to solve the problem.
Black85 has good advice on cleaning the throttle body too.
Black85 has good advice on cleaning the throttle body too.
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