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Old 09-14-2019, 02:35 PM   #1
15A
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Location: OH-MI....just like it sounds
Default 240: Another surging idle question

Helped a friend do a head gasket on an 89 with 210k. Noticed his TPS wasn't clicking so replaced it with one that did. Also replaced his CTS while it was all apart.

Start it up and it runs fine except the idle surges from 1200 to 1700...over and over. Only time I ever had that issue was a reman ECU. Swapped it and it purred. Tried that and no change. TPS is set and the IAC is functioning. My last thought was that 'new' Bosch CTS - new and Bosch mean very little these days. So before I pull the intake off and swap it out with his old one, I unplugged the AMM. Idle went solid (no surging) but at 1600 rpm. Never had an issue with the idle and an AMM.

One more thing.....it throws no codes (which also made me suspect the AMM).

Does this bring back any acid flashbacks of similar-already-figured-out issues anyone here had?

TIA
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Old 09-14-2019, 03:45 PM   #2
dl242gt
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We just had a thread where Art detailed making sure that the throttle switch actually made and breaks. Even though it clicks it has to properly open and close the switch. How is the adjustment of the throttle plate itself? Maybe it is closed or open too much?

The idle control uses the engine rpms as well to regulate. maybe the rpm signal isn't getting to the computer?
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Old 09-14-2019, 04:39 PM   #3
15A
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What I wound up doing for time and my sanity's sake, was to take the complete TB and TPS from a known running car I'm restoring and swap it in. Started and purred like a kitten.

I've had them where just cleaning the encrusted crud out of them caused them to run differently (not necessarily for the better). Also seen the idle was high when the splayed screws had been messed with. You could loosen the screws and slide the throttle plate -maybe- 1/64" (if that) and it would affect idle by 200-300rpms.

I'm overdue for a meeting with Capt Morgan to report my findings

Thanks fellas.
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Old 09-15-2019, 04:51 AM   #4
JW240
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I've had a backfire (caused by another efi issue - bad knock sensor) cause a bent throttle plate. Always check if the valve closes.
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