Intermittent Idle stumble
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Joined: Oct 2003
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From: Houston
Car: 86 Berlinetta 84 MonteCL
Engine: 3.4 MPFI 3.8 229
Transmission: 700r4 T350
Intermittent Idle stumble
Hmmm.....I seem to have developed a slight stumbvle every now and then at idle. It is NOT a misfire (what I mean is, it's not testing as one). It ran fine for a few weeks after the Cam swap a few months ago. Then my O2 sensor threw a code, so I replaced it. I also backed of the timing a hair because I was having starting isssues (thought was timing related, was bad battery/starter). ANyhow, timing was put back up where it ran strong and then I developed a stumble every now and then at idle (feels like intermittent miss). I've tried moving the timing around either direction, doesn't clear up. I plan on trying some colder plugs tommorow, I've been runing 44T's for the 3.4, and I'm gonna try 42's for the 2.8 ignition. ANy ideas what could cause this? I've already ruled out a vac leak.
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Joined: May 2004
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From: Orange, Calif
Car: '87 Cam RS V6
Engine: Top Secret
Transmission: DYT700R4 custom inerts and conv.
Mine will occationally do the same thing on different tanks a gas. Every once in a while I will get a bad load of fuel that will reduce idle rpms on a hot midday idle,or also a warmer nighttime idle(with the lights on of course drawing more juice)
What I have concluded in my case is that the bad fuel will cause the idle to drop slightly enough for me to undercharge and the longer I sit in drive in hot weather, the more the juice drops causing idle stumble, thus resulting in a progressively dropping idle. (90% of fuel loads this never happens- Only an occational bad batch- crappy So. Cal gas with all of the "reformulation" B.S additives they put into it)
I barely add a little pedal at the light and bring the R's up to 900-1000 rpms and it starts to build a charge back and will settle fine again for about 10 seconds after I lift, then voltage drops and the cycle begins again.
If I put my stock crank pulley back on, I gaurantee this would never happen. Pain is the *** when it happens, but it is rare so I right it off. About once every three months the wife will report that the car for no reason out of the blue will just die at a light, sometimes two or three days in a row- Always hot weather outside,but immediately fires right back up. Again, its very rare in my case and I am positive its the fuel.
What I have concluded in my case is that the bad fuel will cause the idle to drop slightly enough for me to undercharge and the longer I sit in drive in hot weather, the more the juice drops causing idle stumble, thus resulting in a progressively dropping idle. (90% of fuel loads this never happens- Only an occational bad batch- crappy So. Cal gas with all of the "reformulation" B.S additives they put into it)
I barely add a little pedal at the light and bring the R's up to 900-1000 rpms and it starts to build a charge back and will settle fine again for about 10 seconds after I lift, then voltage drops and the cycle begins again.
If I put my stock crank pulley back on, I gaurantee this would never happen. Pain is the *** when it happens, but it is rare so I right it off. About once every three months the wife will report that the car for no reason out of the blue will just die at a light, sometimes two or three days in a row- Always hot weather outside,but immediately fires right back up. Again, its very rare in my case and I am positive its the fuel.
Last edited by vsixtoy; Oct 5, 2004 at 02:04 AM.
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Supreme Member
Joined: Oct 2003
Posts: 1,668
Likes: 1
From: Houston
Car: 86 Berlinetta 84 MonteCL
Engine: 3.4 MPFI 3.8 229
Transmission: 700r4 T350
Originally posted by vsixtoy
Mine will occationally do the same thing on different tanks a gas. Every once in a while I will get a bad load of fuel that will reduce idle rpms on a hot midday idle,or also a warmer nighttime idle(with the lights on of course drawing more juice)
What I have concluded in my case is that the bad fuel will cause the idle to drop slightly enough for me to undercharge and the longer I sit in drive in hot weather, the more the juice drops causing idle stumble, thus resulting in a progressively dropping idle. (90% of fuel loads this never happens- Only an occational bad batch- crappy So. Cal gas with all of the "reformulation" B.S additives they put into it)
I barely add a little pedal at the light and bring the R's up to 900-1000 rpms and it starts to build a charge back and will settle fine again for about 10 seconds after I lift, then voltage drops and the cycle begins again.
If I put my stock crank pulley back on, I gaurantee this would never happen. Pain is the *** when it happens, but it is rare so I right it off. About once every three months the wife will report that the car for no reason out of the blue will just die at a light, sometimes two or three days in a row- Always hot weather outside,but immediately fires right back up. Again, its very rare in my case and I am positive its the fuel.
Mine will occationally do the same thing on different tanks a gas. Every once in a while I will get a bad load of fuel that will reduce idle rpms on a hot midday idle,or also a warmer nighttime idle(with the lights on of course drawing more juice)
What I have concluded in my case is that the bad fuel will cause the idle to drop slightly enough for me to undercharge and the longer I sit in drive in hot weather, the more the juice drops causing idle stumble, thus resulting in a progressively dropping idle. (90% of fuel loads this never happens- Only an occational bad batch- crappy So. Cal gas with all of the "reformulation" B.S additives they put into it)
I barely add a little pedal at the light and bring the R's up to 900-1000 rpms and it starts to build a charge back and will settle fine again for about 10 seconds after I lift, then voltage drops and the cycle begins again.
If I put my stock crank pulley back on, I gaurantee this would never happen. Pain is the *** when it happens, but it is rare so I right it off. About once every three months the wife will report that the car for no reason out of the blue will just die at a light, sometimes two or three days in a row- Always hot weather outside,but immediately fires right back up. Again, its very rare in my case and I am positive its the fuel.
Thread Starter
Supreme Member
Joined: Oct 2003
Posts: 1,668
Likes: 1
From: Houston
Car: 86 Berlinetta 84 MonteCL
Engine: 3.4 MPFI 3.8 229
Transmission: 700r4 T350
BUmp, because I still havn't figured it out.
Okay, changed to colder plugs and replaced fuel filter, no help.
Today I spent ripping the upper manifolds and injector rail off. One injector looked abit gummy, so I cleaned it. I also regasketed everything THOROUGHLY! I made sure all vaccumn lines were not leaking and replaced the cold-start injector O-ring (other rings are 1000 miles new). Put it all back together and It still stumbles
. It doesn't have a miss at part throttle, or when it's under load (slight powerbrake trick). I did a balance test and it was inconclusive (got shocked bad 3 times, hand hurts). I am not throwing codes as well. I reset the computer after I finished. I dunno what else it could be (it isn't fuel type). I have a full bottle of nitrous waiting to spurt through my intake and I'm too scared to use it because of this problem. Anyhow, like I said, it isn't missing above 1500 rpm, or when under load, so I may spray it in 2nd gear anyway to test everything out. HELP! :hail:
Okay, changed to colder plugs and replaced fuel filter, no help.
Today I spent ripping the upper manifolds and injector rail off. One injector looked abit gummy, so I cleaned it. I also regasketed everything THOROUGHLY! I made sure all vaccumn lines were not leaking and replaced the cold-start injector O-ring (other rings are 1000 miles new). Put it all back together and It still stumbles
. It doesn't have a miss at part throttle, or when it's under load (slight powerbrake trick). I did a balance test and it was inconclusive (got shocked bad 3 times, hand hurts). I am not throwing codes as well. I reset the computer after I finished. I dunno what else it could be (it isn't fuel type). I have a full bottle of nitrous waiting to spurt through my intake and I'm too scared to use it because of this problem. Anyhow, like I said, it isn't missing above 1500 rpm, or when under load, so I may spray it in 2nd gear anyway to test everything out. HELP! :hail: 
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