Funky idle with 350 tbi swap
04-29-2018, 09:37 AM
#1
Junior Member
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Funky idle with 350 tbi swap
Hey guys,
I’m dealing with an odd issue with my 91 RS. It’s been swapped with an unknown 350 before I bought it. I don’t know all that’s been updated, but an odd issue just started occurring. I noticed a funky idle issue when the car was cold and also noticed the plug wires were randomly popping off and arcing. So, I decided to replace the wires, cap, rotor and found that one of the wires (#6) was rubbing against the header and wires were exposed. Whoops!! So, after that, I still had the same issue. I read that a bad ECM could cause irratic idle issues and I had an extra one laying around (from a 91 Caprice) and swapped them this morning. Disconnected battery, swapped ECM, reconnect battery, and BOOM the idle issue was gone. Instead I have a super-fast Check Engine light blinking constantly. I guess my options are to diagnose the blinking/ghosting Check Engine light or get another ECM from a 91 RS. Thoughts??
I’m dealing with an odd issue with my 91 RS. It’s been swapped with an unknown 350 before I bought it. I don’t know all that’s been updated, but an odd issue just started occurring. I noticed a funky idle issue when the car was cold and also noticed the plug wires were randomly popping off and arcing. So, I decided to replace the wires, cap, rotor and found that one of the wires (#6) was rubbing against the header and wires were exposed. Whoops!! So, after that, I still had the same issue. I read that a bad ECM could cause irratic idle issues and I had an extra one laying around (from a 91 Caprice) and swapped them this morning. Disconnected battery, swapped ECM, reconnect battery, and BOOM the idle issue was gone. Instead I have a super-fast Check Engine light blinking constantly. I guess my options are to diagnose the blinking/ghosting Check Engine light or get another ECM from a 91 RS. Thoughts??
04-29-2018, 12:40 PM
#3
Junior Member
Thread Starter
Re: Funky idle with 350 tbi swap
That may very well be! I used the existing prom but I have no idea if it's the stock one or not. I also have no idea if it's been modified. Also, plot twist, I drove the car with the swapped ECM and existing prom for about 3 minutes or so and one of the plug wires on the drivers side started to smoke...could have been the plug, but it was waaaaaay odd. I'm sure it was tune related. I swapped back to the original ECM and the smoking quit.
04-29-2018, 12:47 PM
#4
Re: Funky idle with 350 tbi swap
The ecm should be a 1228746 service number. If the prom is put in a different service number ecm it runs in a limp home mode (runs rich).
The caprice one should be a anlu or atjp in prefer to work in your ecm.
Unless it’s a custom tune it might work.
Have you checked your fuel pressure, sounds like it was lean and adding fuel resolved the issue.
The caprice one should be a anlu or atjp in prefer to work in your ecm.
Unless it’s a custom tune it might work.
Have you checked your fuel pressure, sounds like it was lean and adding fuel resolved the issue.
05-01-2018, 01:47 PM
#5
Junior Member
Thread Starter
Re: Funky idle with 350 tbi swap
I haven't checked the pressure lately, but I believe it was checked about 4 months ago when it was in the shop. 12 psi. I've been putting off the new fuel pump, but it might be time. I'm picking up a replacement ECM this weekend to see if it helps the issue. I also read that the MAP sensor could create odd idle issues, too. When the car's cold, the rpms drop, car almost stalls, the rpms pop back up, but don't hold. Rpms drop again and the car seems like it's choking. This happens until the temp gets to 150/180 or so.
05-01-2018, 03:18 PM
#7
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05-09-2018, 08:31 AM
#9
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Re: Funky idle with 350 tbi swap
Hmmm, alright... well, I started questioning if the MAP sensor was working, so while the car was running, I disconnected it. The car died immediately. I assume that means the MAP is operating just fine. Is that safe to assume? I took a video of what the car's doing and uploading it right now. Hopefully someone can point me in the right direction. I'll post a link shortly.
On a side note, would bad spark plugs cause this issue? The other day, I replaced the plug wires, cap, and rotor, but not the plugs. I'm just spitballing here, but unless they're getting fouled, that shouldn't be the case, right? I guess replacing them doesn't hurt. It just seems like there's a sensor bad somewhere. The car doesn't actually die, it just wants to. Looking for threads to pull.
On a side note, would bad spark plugs cause this issue? The other day, I replaced the plug wires, cap, and rotor, but not the plugs. I'm just spitballing here, but unless they're getting fouled, that shouldn't be the case, right? I guess replacing them doesn't hurt. It just seems like there's a sensor bad somewhere. The car doesn't actually die, it just wants to. Looking for threads to pull.
05-09-2018, 10:13 AM
#10
Junior Member
Thread Starter
Re: Funky idle with 350 tbi swap
Video link: The tach doesn't work (SHOCKER!) and the oil pressure is reading really high. The car will continue to do this until it's warm (180 or so). Could use any and all ideas/suggestions. Thanks.
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