HELP idle/drivability issues
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 1,032
Likes: 197
From: Atoka, TN
HELP idle/drivability issues
i bought this 86 coupe a few months ago and it had issues. so i went about fixins some stuff. i pulled the intake to fix an oil leak, changed the egr and injectors(because i was there), changed the egr temp switch(because it was giving me a SES light), changed the maf relays(because they were giving SES also), changed the 02 sensor(why not), and changed the IAC because the car was idling like it was hunting(i cleaned the TB, too). the timing is set to 6 degrees, i cut the air lid, gutted the precats, installed a new main cat, and eliminated the mufflers. my fuel pressure is 38 with engine off and 36 at idle. i also set the minimum idle to 450 in park and adjusted the tps to .55.
now the car "hunts" at idle(just like before). when i took it for a little spinn, it started missing throughout the driving range( 0-45mph). you could here it in the exhaust and feel it bad. i have been using the haynes, TPI swappers guide and the 86 corvette shop manual to trouble shoot this. please give me some ideas on where to go next.....i am lost.
chris
now the car "hunts" at idle(just like before). when i took it for a little spinn, it started missing throughout the driving range( 0-45mph). you could here it in the exhaust and feel it bad. i have been using the haynes, TPI swappers guide and the 86 corvette shop manual to trouble shoot this. please give me some ideas on where to go next.....i am lost.
chris
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
When you replaced the IAC did you clean the bore under the TB and reset base idle to 450rpm?? Also, check for any vacuum leaks as they will cause hunting idle.
Since you are getting a miss at idle, clip a timing light in turn onto each spark plug wire to see if missed flashes coinside with engine misses. If you find a bad wire, check the wire, spark plug and dist cap.
Is the ECM throwing any codes.
Since you are getting a miss at idle, clip a timing light in turn onto each spark plug wire to see if missed flashes coinside with engine misses. If you find a bad wire, check the wire, spark plug and dist cap.
Is the ECM throwing any codes.
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 1,032
Likes: 197
From: Atoka, TN
yes, i cleaned the bore the IAC screws into. including the seat that the IAC pintle goes against. i measured the length of the valve and it was less than 1 & 1/8 inches. then i followed the procedures on your site to set the base idle and tps voltage. i did the look under the hood check after my drive to see if there was any arching and saw nothing. i looked at the cap and rotor when i pulled the distributor for the intake leak, they looked new. i will try the timing light test in the morning and if the boss lets me, i might spring for a new set of plugs and wires too.
i am not getting any ecm codes. i guess the computer thinks all is well.
i am not getting any ecm codes. i guess the computer thinks all is well.
Last edited by cmashark; Jul 2, 2005 at 12:15 AM. Reason: no ecm codes
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Try the plugs and wires (AC Delco plugs, no need to go expensive) and if it is still missing, throughly check for vacuum leaks with carb cleaner/propane. Look for any of the small hoses/lines off or cracked (the hard plastic vacuum lines like to crack with age).
Race Director
Joined: Jul 2001
Posts: 14,604
Likes: 3
From: Glendale, AZ
Originally Posted by Morley
Try the plugs and wires (AC Delco plugs, no need to go expensive) and if it is still missing, throughly check for vacuum leaks with carb cleaner/propane. Look for any of the small hoses/lines off or cracked (the hard plastic vacuum lines like to crack with age).
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Originally Posted by Togo
not to nitpick, wouldn't you rather use starting fluid instead of carb cleaner? just curious as personally i would assume that carb cleaner might "kill" idle, and starting fluid should increase it. - then again either should prove the point - so just disregard what i said, i'm an idiot!
Race Director
Joined: Jul 2001
Posts: 14,604
Likes: 3
From: Glendale, AZ
Originally Posted by Morley
One would think so but carb cleaner is very flamable...but not like starting fluid (ether) which is bordering on explosive.
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Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 1,032
Likes: 197
From: Atoka, TN
Update
ok, well i found no vacuum leaks and i used starting fluid. tried the timing light on all plug wires and all was good there. so i decide to pull the plugs.......2 plugs had ZERO GAP??????!!!!!!! so did a compression test and all cylinders were 165 +/- 2psi.(i guess thats good). i replaced all 8 autolites with cheapie A/C Delcos, redid the base idle and tps adjustments. this thing moves!!!!! 
drove it about 3 miles around town and then took it on the HWY for a 75mph run. temps stayed about 185ish and never missed a beat.
thanks 65ZO1, morley and togo.
chris
drove it about 3 miles around town and then took it on the HWY for a 75mph run. temps stayed about 185ish and never missed a beat.thanks 65ZO1, morley and togo.
chris
Thread Starter
Burning Brakes
Joined: Apr 2004
Posts: 1,032
Likes: 197
From: Atoka, TN
Originally Posted by Morley
Were the plugs with no gap in hard to reach places? If so, the person that installed them probably dropped them a time or 2 and didn't check the gap again when they picked them up.
no, they were cylinders 2 and 4. definately the 2 easiest. and the threaded area was kinda long compared to the A/C delcos i just put in. thats why i did the compression test. was 165 +/- 2psi good for all of my cylinder pressures? the car has 82k on it.
chris
