rough idle
06-16-2018, 10:36 PM
#1
Advanced
Thread Starter
rough idle
Just put new plugs, wires, cap, rotor, ignition module, in my 84 cross fire. Idle is rough, falls to 400 to 500 when coming to a stop. Will be checking for vacuum leaks tomorrow morning. Yes plugs are in the right order. Seems to smooth out at a higher rpm. What am I overlooking ?
06-17-2018, 09:18 AM
#2
Zen Vet Master Level VII
Actually 400-500 is factory spec for those cars. Seriously I don't get it either, but it is.
Vacuum leaks will make your engine run "higher" so I don't think this is the issue.
If you want your idle up a bit, an easy and quick "cheat" is bump your timing up to somewhere from 8-12 depending on what your car likes. Through trial and error, I found my XFire LOVED 12. Mine idled at about 750ish but the AC and sitting at a stop brought it down to 550.
Vacuum leaks will make your engine run "higher" so I don't think this is the issue.
If you want your idle up a bit, an easy and quick "cheat" is bump your timing up to somewhere from 8-12 depending on what your car likes. Through trial and error, I found my XFire LOVED 12. Mine idled at about 750ish but the AC and sitting at a stop brought it down to 550.
Last edited by billschroeder5842; 06-17-2018 at 09:19 AM.
06-17-2018, 02:32 PM
#3
Advanced
Thread Starter
Actually 400-500 is factory spec for those cars. Seriously I don't get it either, but it is.
Vacuum leaks will make your engine run "higher" so I don't think this is the issue.
If you want your idle up a bit, an easy and quick "cheat" is bump your timing up to somewhere from 8-12 depending on what your car likes. Through trial and error, I found my XFire LOVED 12. Mine idled at about 750ish but the AC and sitting at a stop brought it down to 550.
Vacuum leaks will make your engine run "higher" so I don't think this is the issue.
If you want your idle up a bit, an easy and quick "cheat" is bump your timing up to somewhere from 8-12 depending on what your car likes. Through trial and error, I found my XFire LOVED 12. Mine idled at about 750ish but the AC and sitting at a stop brought it down to 550.
06-17-2018, 06:11 PM
#4
Zen Vet Master Level VII
Can you put a gauge on your fuel rail? You need at least 11 to be happy.
06-17-2018, 07:41 PM
#5
Safety Car
There's no fuel rail in an '84. It's a good idea to check your fuel pressure, and an easy way to do that is to remove your fuel filter and put a "T" in a piece of fuel hose that's installed in the place of the fuel filter. That's not quite as accurate as a special fuel pressure adapter between the throttle bodies, but it's a good test.
06-17-2018, 08:52 PM
#6
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Hi !!
I’m a C5 guy but as a “diagnostic hobbyist” it looks like it can be a vacuum leak...these problems like you mentioned is that the car ran better at higher RPM...I use fuel trims to diagnose this issue. I use a higher end scan tool and a lab scope and these 2 pieces of equipment are ESSENTIAL to accurate diagnostics...you can use propane (my method), brake clean, or even water to find the vacuum leak...it also sounds like possibly a MAF sensor...I believe on the C4’s the MAF voltage is .4 volts at idle and 5 volts at WOT...maybe someone with a C4 FSM can confirm my numbers but before you do anything with the MAF sensor VERIFY CIRCUIT INTEGRITY !!... I just helped a C5 owner last week that had a MAF DTC and he replaced the MAF sensor but he still had the DTC set. He was going to go and replace it again but I had him check the wiring...he had no 5 volt reference voltage at the connector...he found a badly chaffed wire and after he replaced it everything was HUNKY DORY...hope this might help and happy Fathers Day !!
I’m a C5 guy but as a “diagnostic hobbyist” it looks like it can be a vacuum leak...these problems like you mentioned is that the car ran better at higher RPM...I use fuel trims to diagnose this issue. I use a higher end scan tool and a lab scope and these 2 pieces of equipment are ESSENTIAL to accurate diagnostics...you can use propane (my method), brake clean, or even water to find the vacuum leak...it also sounds like possibly a MAF sensor...I believe on the C4’s the MAF voltage is .4 volts at idle and 5 volts at WOT...maybe someone with a C4 FSM can confirm my numbers but before you do anything with the MAF sensor VERIFY CIRCUIT INTEGRITY !!... I just helped a C5 owner last week that had a MAF DTC and he replaced the MAF sensor but he still had the DTC set. He was going to go and replace it again but I had him check the wiring...he had no 5 volt reference voltage at the connector...he found a badly chaffed wire and after he replaced it everything was HUNKY DORY...hope this might help and happy Fathers Day !!
06-18-2018, 06:53 PM
#7
Advanced
Thread Starter
I think I have the idle problem figured out. NO vacuum leaks. Voltage is correct where it should be. It is running very rich at idle. Can smell it and getting light puffs of black out of the exhaust. So at this point I'm thinking Idle Air Control Valves. Can these be cleaned and reset? Have done one on a 2bbl TBI 305 engine. I assume these would be the same except there are 2 of them?