Wierd Idle Surging and Misfiring
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
Likes: 0
From: Glen Rock, PA
Wierd Idle Surging and Misfiring Ive been dealing with a odd problem where the car starts up completely fine, then after 5 minutes or so the engine idle will begin to bounce up and down and if i try revving it, all it does is misfire like crazy. Its pretty much undriveable when this happens. Ive been monitoring things through Freescan and everything seems perfectly fine. No code thrown except my EGR (LT Headers). Im going to list everything ive replaced below and you can comment on what else could be the cause. Every once in a while it will act perfectly ok but 90% of the time it will have the erratic surging and misfiring. Im to the point that i think its the PCM because i dont know what else to check.
IACV (Reset using shbox instructions)
CTS
Plugs
Wires
Optispark
Fuel Injectors (Leak Proof and Resistance Tested Fine)
Fuel Filter
Fuel Pump
Oxygen Sensors
Coil
IACV (Reset using shbox instructions)
CTS
Plugs
Wires
Optispark
Fuel Injectors (Leak Proof and Resistance Tested Fine)
Fuel Filter
Fuel Pump
Oxygen Sensors
Coil
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
Likes: 0
From: Glen Rock, PA
Tried that already as well. Ive also tried looking for any vacuum leaks and there arent any that i can find. This issue has been a real PITA. I replaced the CTS on saturday and the car ran great for 90 miles then all of a sudden started doing it again. It was a NAPA part so i dont think it could go bad that quickly.
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
Likes: 0
From: Glen Rock, PA
No tune. Headers and dual exhaust is all I have done. It ran solid for about 3 months after the mods then all of a sudden started doing this off and on and now it's 90% of the time. I'm going to clean the PCM ground and ground the block to the chasis just to be sure the PCM is getting a solid ground. If that doesn't do it, I have no idea.
Teching In
Joined: Feb 2013
Posts: 37
Likes: 0
From: Pennsylvania
I was having the same problem with my 94z. All I did was change the fuel filter and ran some seafoam through it. Ran fine after that. I don't know if it actually helped with anything, or I just got lucky. Worth a shot though.
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
Likes: 0
From: Glen Rock, PA
Ill add some seafoam to the gas tomorrow and see what happens. Ive ran other fuel system cleaners in previously and the problem hasnt gone away. Fuel filter has been replaced. Its definitly getting plenty of fuel. Once the idle issue starts it will burn up some gas in no time at all.
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Launching!
Joined: Apr 2012
Posts: 233
Likes: 0
From: Crown point, IN
Ive been dealing with a odd problem where the car starts up completely fine, then after 5 minutes or so the engine idle will begin to bounce up and down and if i try revving it, all it does is misfire like crazy. Its pretty much undriveable when this happens. Ive been monitoring things through Freescan and everything seems perfectly fine. No code thrown except my EGR (LT Headers). Im going to list everything ive replaced below and you can comment on what else could be the cause. Every once in a while it will act perfectly ok but 90% of the time it will have the erratic surging and misfiring. Im to the point that i think its the PCM because i dont know what else to check.
I have an underlining feeling that it's a possible ground issue.
Let us know what you find out!
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
Likes: 0
From: Glen Rock, PA
I only had a 1/4 can of seafoam around so I added some to the gas and ran some through the intake. It was idling like **** when i put it in. Turned the car off for around 15 minutes then restarted running smooth. After I get home from work tonight I'll start it up again and see what happens. Would be nice if the problem is solved but I still feel I had a lucky start up. I picked up 2 cans of seafoam to use with a full tank of gas and run alot more through the intake.
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
Likes: 0
From: Glen Rock, PA
Put the seafoam in the gas tonight and let it run a while. Started doing the surging. I wish I had a wideband so I could see the AFR. I'm wondering if the headers and dual exhaust can actually cause it to run lean enough to create the surging? It just seems odd that it will run fine sometimes and surge at others.
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
Likes: 0
From: Glen Rock, PA
Im going to send the PCM in for tuning. The car has been able to become driveable after reaching full operating temp. Drives with alot of pop in the exhaust and little low end tq. Runs smooth but not torquey smooth like it should be. Im thinking it needs to be richened up and that warm up cycle before the 02's become active is really lean at the moment causing the idle bounce and missfire. Ill let everyone know how it is when PCMForLess gets me the PCM back.
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
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From: Glen Rock, PA
Got the PCM back. Idles very smooth for a while then develops a slight bounce in the idle. It drives with a slight missfire but not nearly as bad as before. Im going to change plugs and if that doesnt do it, then ill be pulling the optispark for inspection. My gut is telling me its the optispark fouling up. I took the gamble on a Jegs unit first time around, i wont gamble on that again. Delphi will go in if the plugs arent the problem. The plug wires i have are Jegs as well. Anybody have any bad experiences with these?
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
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From: Glen Rock, PA
Now the question is what from the Opti is causing the misfire? Is it the optical sensor misreading the timing? Or is it a combination of bad cap and rotor not firing the plugs? GM really F'd up bad when they made the optispark.
Launching!
Joined: Aug 2012
Posts: 259
Likes: 0
From: Johnstown, Pa
Got the PCM back. Idles very smooth for a while then develops a slight bounce in the idle. It drives with a slight missfire but not nearly as bad as before. Im going to change plugs and if that doesnt do it, then ill be pulling the optispark for inspection. My gut is telling me its the optispark fouling up. I took the gamble on a Jegs unit first time around, i wont gamble on that again. Delphi will go in if the plugs arent the problem. The plug wires i have are Jegs as well. Anybody have any bad experiences with these?
Have you checked your ICM they will cause problems when they heat up. Shoebox has a real good explanation how exactly to check it. Also even though the lt1s don't have a timing indicator you could still hook up a light and see if the spark is consistent on each cyl so you don't have to yank the opti and pray its the problem. Just move your timing gun on each cyl and make sure they are all firing in a pattern
Thread Starter
Launching!
Joined: Jun 2008
Posts: 242
Likes: 0
From: Glen Rock, PA
Im going to space out the ICM tomorrow and also hook the timing light on each plug wire to see how it reacts. It seems to break down the most once warmed up so it could be a good chance of being a bad ICM.