89 TPI runs rough when cold
Thread Starter
Safety Car
Joined: May 2002
Posts: 4,010
Likes: 26
From: Somewhere nowhere
89 TPI runs rough when cold
my 89 TPI runs rough when cold. it idles rough & hesitiates.
when it's warm, it runs great.
It has new injectors, new EGR, new PCV, new cap rotor, no codes.
Is there something specific I should look at?
when it's warm, it runs great.
It has new injectors, new EGR, new PCV, new cap rotor, no codes.
Is there something specific I should look at?
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Vacuum leaks! Mine ran rough and hunted for idle when in open loop (<140*) and settled out after it warmed up. There are a few different methods to check for vac leaks. Propane, WD-40, starting fluid, Seafoam, smoke in the intake. Basically, as soon as the O2 sensor starts sending voltage readings to the ECM the odd idling will stop. If not vac leaks, clean the TB and IAC, check voltage on the TPS, and Make sure the AIR system and MAF is operating correctly. Check the connections.
Last edited by RRT vette; Jul 4, 2007 at 11:10 PM.
Drifting
Joined: Mar 2004
Posts: 1,500
Likes: 1
From: Mauldin sc
St. Jude Donor '05
Last edited by golfman2008; Sep 1, 2007 at 02:41 AM.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
cold only
my 86 was doing that, and I changed the electronic spark control over by the heater, and it idles smooth now when cold. I also installed an adjustable pressure regulator and cranked up the pressure to 40 with the vacuum line on, and 45 without it.
other things to check are:
plug wires,
distributor cap,
the accordion inlet duct for leaks,
loose clamps on that duct,
cracked or broken vacuum hoses under the plenum,
loose connector on the map,
Egr valve,
timing,
partially plugged precats, or cat.
other things to check are:
plug wires,
distributor cap,
the accordion inlet duct for leaks,
loose clamps on that duct,
cracked or broken vacuum hoses under the plenum,
loose connector on the map,
Egr valve,
timing,
partially plugged precats, or cat.
Last edited by coupeguy2001; Jul 6, 2007 at 01:20 AM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Coolant Temp Sensor is used in place of a choke and if yours is indicating the engine is warmed up, it'll be too lean when it's cold. Best to check with a scanner as it could also be a faulty ECM. You can buy another sensor and simply plug it into the harness. If it starts up and idles ok, R & R the old one. Other clues would be the fan running with it cold - a/c off; no fast idle.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
regulator
screw it in to increase, out to decrease.
Remember, 89 was the first year they did away with the cold start injector, and reprogrammed the chip to increase fuel from the injectors when cold.
I would hazard a guess, that either the sensor (CTS) is sending erroneous info, or the engine has a weak ground, or there is a weak injector.
Also, to increase the fuel, the idle has to go up also. Check the IAC passages for restrictions. Also, when cold, the spark plug wire resistance changes. If there is a break in a plug wire, the core shrinks a little, causing extra gaps in the wire making the resistance really high.
Also, check for the proverbial cracked distributor cap, or a cap with lots of carbon tracking.
Remember, 89 was the first year they did away with the cold start injector, and reprogrammed the chip to increase fuel from the injectors when cold.
I would hazard a guess, that either the sensor (CTS) is sending erroneous info, or the engine has a weak ground, or there is a weak injector.
Also, to increase the fuel, the idle has to go up also. Check the IAC passages for restrictions. Also, when cold, the spark plug wire resistance changes. If there is a break in a plug wire, the core shrinks a little, causing extra gaps in the wire making the resistance really high.
Also, check for the proverbial cracked distributor cap, or a cap with lots of carbon tracking.
Last edited by coupeguy2001; Aug 31, 2007 at 06:27 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
