Rough idle problem
Thread Starter
Advanced
Joined: May 2016
Posts: 55
Likes: 2
From: Lewes Delaware
Rough idle problem
When sitting at idle, car acts like it is loading up and surging. As soon as I give it gas it stops. No miss while riding along, just when I come to a stop. Acts like it is trying to cut out. Using high test gas. Anyone have any ideas? Would appreciate help.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Do a minimum idle adjustment:
https://www.corvetteforum.com/forums...post1570563689
Also you need to check for vacuum leaks, which can cause a rough idle.
https://www.corvetteforum.com/forums...post1570563689
Also you need to check for vacuum leaks, which can cause a rough idle.
Team Owner
Joined: Jul 2004
Posts: 28,376
Likes: 3,260
From: Hartford WI
Get a scanner and see what the IAC counts are. 20 to 30 is the target range. If they are at 0 and you turn the adjustment screw out, rev it and it still settles down at 0, repeat. When it is all the way out and still at 0, you have a leak. Find leak. Clean the TB by disconnecting everything, take the top plate out, take the IAC out, take the IAC housing out and clean all with brake cleaner including the passages. Be very gentle with the IAC. Spray pintle and gently wipe. Reassemble with fresh gaskets and retest.
You can also check the Coolant Temp Sensor. See if it is reading a plausible number. Scan the CTS with an infra red gun at cold and hot temp. At the same time, you should check the scanner to see what it is doing for CTS reading. They should be very close.
Also check your timing. It should be around 6 degrees. Make sure that your harmonic balancer is not walking around on you.
Assuming spark is good, check fuel pressure. It should be around 43 psi when you turn on. It should hold pressure for a couple of hours. Move on to testing what it is when you hit a WOT run. It might drop a second but it should go up to 43 which tells you that the pump can deliver.
You can also check the Coolant Temp Sensor. See if it is reading a plausible number. Scan the CTS with an infra red gun at cold and hot temp. At the same time, you should check the scanner to see what it is doing for CTS reading. They should be very close.
Also check your timing. It should be around 6 degrees. Make sure that your harmonic balancer is not walking around on you.
Assuming spark is good, check fuel pressure. It should be around 43 psi when you turn on. It should hold pressure for a couple of hours. Move on to testing what it is when you hit a WOT run. It might drop a second but it should go up to 43 which tells you that the pump can deliver.
Safety Car
Joined: Aug 2009
Posts: 3,745
Likes: 275
From: Melbourne, Victoria, Australia
Thread Starter
Advanced
Joined: May 2016
Posts: 55
Likes: 2
From: Lewes Delaware
1994 convertible new msd vented distributor, icm, coil, all in last 6months. Mechanic put new coolant temp sensor in today because he said the car thinks it is in Alaska. He referenced a reading of it thinks it is 34 degrees outside. Scanner told him something about an oil temp sensor maybe. After putting in the coolong temp sensor it still idled rough.
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Team Owner
Joined: Jul 2004
Posts: 28,376
Likes: 3,260
From: Hartford WI
1994 convertible new msd vented distributor, icm, coil, all in last 6months. Mechanic put new coolant temp sensor in today because he said the car thinks it is in Alaska. He referenced a reading of it thinks it is 34 degrees outside. Scanner told him something about an oil temp sensor maybe. After putting in the coolong temp sensor it still idled rough.
Burning Brakes
Joined: Dec 2005
Posts: 805
Likes: 11
From: Hickory Flat Ga
Find yourself somebody that can run an OBD1 scanner and pay the charge. That will be your quickest and cheapest solution. There are simply too many possible causes to guess and throw parts at.
Also come back and tell us the fix. It makes for good forum reading.
Also come back and tell us the fix. It makes for good forum reading.
Last edited by tlong; Oct 11, 2016 at 11:36 PM.
Thread Starter
Advanced
Joined: May 2016
Posts: 55
Likes: 2
From: Lewes Delaware
I put a new MSD distributor in less than 6 months ago. Mechanic showed me moisture in it. How and why is a mystery to me. I thought this vented distributor was supposed to be the fix after having put two non vented ones in in the last year and a half. I think it is time to buy another vette.