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1989 7MGTE Ice Blue Pearl,
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47 Posts
Discussion Starter · #1 · (Edited)
So after doing my swap/rebuild/ 550cc, Lex AFM, 57 Trim ct26, Driftmotion Downpipe and intercooler kit but with stock recirc, 3 inch straight pipe exhaust. I have had an idle issue and cant seem to find the issue. I know this is a common thing with the 550s and lex, but thought peoples cars at least stayed running. When cold the car starts and idles fine but as it warms up it will start to hunt and then die out. Here are some of the things I have tried.

No codes in ECU but when revved up to 2,500rpm I will get a 52 ( knock Sensor ). Will this affect idle even with this cleared and not stored?
Checked and rechecked timing. ( at about 10 to 11 when jumpered )
Checked for Intake and Vacuum leaks. ( No leaks found )
New 02 Sensor
New ECU Temp sensor ( Autozone not OEM )
Aeromotive FPR set to Stock Settings Per TSRM
Tested IAC per TSRM ( seems to click when manual checking each pin ) Also clicks the right amount when turning the car off.
Stock AFM ( wideband read 20+ at idle vacuum shows around 15 to 17 inhg ), Drove it and AFRs in 13 to 14 range. Had to stay on throttle to keep it from dying. Stayed out of boost. Car felt strong but again would not idle. If I unplug the AFM car idles great and wideband shows 11.5 to 12, vac at 21 to 24 inhg. Tried an Lex AFM and it read/did the same as the stock AFM. Checked AFM wiring to ECU per TSRM everything was good.

At this point I decided to make sure my TPS was set per TSRM. Checked it and was fine but moved it and set it back again. No change. I found it hard to believe I may have had 2 bad AFM's but decided to order a new lex AFM anyways and put it on the car it now reads PIG RICH ( 10+ AFR ) although much better idle it still will die out most of the time. Checked Plugs they are all firing and are really sooty so are most likely fouled. Gonna put new ones in before I start it next time. I have a Apexi Neo but found out it has the wrong software so was never able to put it on the car. Not sure if taking fuel out would help this or not?

Any ideas of something I missed or should look at next? Thanks!
 

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1989 7MGTE Ice Blue Pearl,
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47 Posts
Discussion Starter · #2 ·
No Ideas?
 

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On a properly leak free system, it is not an issue of the lex/550 combo. It will be a leak issue either on the accordian hose going to the lex or to the turbo. where that "hose" has turned hard and usually ends up cracking. Other places, IACV, Blow Off Valve.

On the leak check, how did you check?

In the end, doing the lex/550 combo uses some low level values within the TCCS that were never designed to be used as the iginition timing is on the stupid side of aggressive leading to detonation/knock. Overall it is not a good idea any more to do the lex/550 with all the information around it.
 

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1989 7MGTE Ice Blue Pearl,
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47 Posts
Discussion Starter · #4 ·
Sorry forgot in the op that I have a brand new accordian hose on the car. Bought it when dropping in the engine back in sept. Also, I know its not the best but we went around with our hands and then also brake clean to see if it idled up anywhere and it did not. Many hours double checking for leaks. My next plan was to do a proper intake to TB leak test but have not done it yet. Also I have easy access to and AEM v2 but have not put it on the car yet. Wanted to make sure it ran properly with stock ECU before switching. So as far of worrying about timing that shouldn't be as much of an issue when going to the AEM ?
 

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89 Turbo - 2JZGE-T VVti (build/swap in progress)
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I had a very similar problem (bad idle, lean cruise, died all the time), and I never really found the cause. I did a compression test and it turns out cylinder 6 was dead (low compression). I'm unsure if that was the cause, or a side effect of whatever was wrong and me boosting around despite it running like shit. I also boosted a few times on really old fuel because I'm retarded

Have you tried reading the Vf (fuel correction) value when it's warm? It sounds to me like it starts having problems as it enters closed loop mode and starts trying to adjust fuel based on the o2 feedback/AFM input.
Here's a good guide to understanding the Vf trim:
I'll bet you it's doing some crazy shit like pulling fuel while the AFR's 15+.

My blind guess is a wiring issue fucking with the ECU's closed loop inputs:
Coolant temp
AFM
O2
Since you already replaced the sensors, that would leave either the wiring or the ECU. I suggest following the signal wire back from each sensor, carefully inspecting them for cracked/brittle areas that could possibly muddy the signal the ECU received.

Another possibility could be an ignition problem. I suggest taking a timing light and putting the pickup on each plug wire. If there's one with a more erratic blinking, it could point to bad coil packs. 7M coils are 30+ years old now and are known have micro cracks that mess with them.
 
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