1985 standard equipment erratic idle
Thread Starter
Racer
Joined: May 2011
Posts: 346
Likes: 3
1985 standard equipment erratic idle
Ok my Vette just suddenly decided to get a case of the erratic idles. A little backround its a 1985 all stock. I have replaced the plugs, wires, cap, rotor, and thermostat. I also cleaned the Thottle Body, IAC, and IAC housing. The IAC was absolutly cruddy and was so bad I had to lightly hit the tip with a cooper wire brush to clean it. That was 3 weeks ago.
This is only an idle problem when driving under normal conditions the car runs great.
It started yesterday I went to start it and it started wierd kind of rough and stumbling. Then it came up to to normal idle and the SES light popped on. I drove it to the bank and it got up to normal operating temps. and ran great. Shut it down and went into the bank and when I cam eout and started it. It started normal and the SES light was out. Drove it home and it was fine.
Today I started it and again same rough start and SES light. I drove it and again it was ok. Shut it down took my kid to guitar practice and when I came out it started fine. This time though when I was driving it the car was searching for idle and dipping real low. sometimes down to 470 rpm. My car usually idles at 550-610 RPM's when hot and in gear. I always thought the idle was a little rough since I got it.
This is only an idle problem when driving under normal conditions the car runs great.
It started yesterday I went to start it and it started wierd kind of rough and stumbling. Then it came up to to normal idle and the SES light popped on. I drove it to the bank and it got up to normal operating temps. and ran great. Shut it down and went into the bank and when I cam eout and started it. It started normal and the SES light was out. Drove it home and it was fine.
Today I started it and again same rough start and SES light. I drove it and again it was ok. Shut it down took my kid to guitar practice and when I came out it started fine. This time though when I was driving it the car was searching for idle and dipping real low. sometimes down to 470 rpm. My car usually idles at 550-610 RPM's when hot and in gear. I always thought the idle was a little rough since I got it.
Thread Starter
Racer
Joined: May 2011
Posts: 346
Likes: 3
I picked one of these but I have no idea how to test the TPS. I have read that you need a multi meter but I have no idea how to use one. I'm a rookie with sensors.
http://cgi.ebay.com/ebaymotors/TPS-T...Q5fAccessories
http://cgi.ebay.com/ebaymotors/TPS-T...Q5fAccessories
Team Owner
Joined: Jan 2003
Posts: 20,324
Likes: 250
From: Summerland B.C. Canada
When you get your TPS harness, you will be measuring the DC voltage of the top 2 wires on TPS. Black probe on top wire, red probe on middle wire.
Lots of vids on how to use a meter.
http://www.google.ca/search?q=how+to...iw=960&bih=403
Code info from my 86 FSM.
http://members.shaw.ca/corvette86/Code%2042.pdf
http://members.shaw.ca/corvette86/Code%2043.pdf
Lots of vids on how to use a meter.
http://www.google.ca/search?q=how+to...iw=960&bih=403
Code info from my 86 FSM.
http://members.shaw.ca/corvette86/Code%2042.pdf
http://members.shaw.ca/corvette86/Code%2043.pdf
Thread Starter
Racer
Joined: May 2011
Posts: 346
Likes: 3
Ok I looked over the initial start-up procedure the car goes through when it starts. Looks like it checkes the knock sensor during start up. I'm thinking maybe my knock sensor is reporting a knock and then retarding the timing? Sound plausable?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Racer
Joined: May 2011
Posts: 346
Likes: 3
I hope he chimes in I know is nothing but a damn sensor the car runs awsome other than the SES and erratic idle. I am so desperate I am reduced to taking to a local stealership that has OBD equipment that can still read a 1985 and datastream it.
Team Owner
Joined: Jan 2003
Posts: 20,324
Likes: 250
From: Summerland B.C. Canada
Thread Starter
Racer
Joined: May 2011
Posts: 346
Likes: 3
Hey all quick update on this problem in case anyone runs into it. I had three problems which all compounded.
1.) The timing was way off it was 32 degrees advanced.
2.) The IAC was totally shot, which explains the erratic idle it was hunting 480-580-620 pattern.
3.) When I bypassed the TB water jacket I ran it right under the IAC which was overheating it.
He said it looks like someone replaced onee of the computers or sensors (he told me but I can't remember which) and they must have advanced the timing before swapping it. After swapping it they forgot to reajust the timing back. So I drove it tonight and WOW this car runs amazing now! Better than it has since I owned it.
1.) The timing was way off it was 32 degrees advanced.
2.) The IAC was totally shot, which explains the erratic idle it was hunting 480-580-620 pattern.
3.) When I bypassed the TB water jacket I ran it right under the IAC which was overheating it.
He said it looks like someone replaced onee of the computers or sensors (he told me but I can't remember which) and they must have advanced the timing before swapping it. After swapping it they forgot to reajust the timing back. So I drove it tonight and WOW this car runs amazing now! Better than it has since I owned it.
