Fixed_____'95 Monte Z34 Erratic idle/bucking in cruise

[jb88ci]

Hey all,

turned out to be an bad plug lead. The terminal had come off the plug end under the boot.



I've read thru some posts to try and pinpoint this but haven't found a good answer.

1995 Monte Z34 (3.4 DOHC) 133,000 Km. Brand new air filter, PVC valve and fuel filter, wires appear newer and are not brittle, don't know when plugs were last changed...only had car for a month, 3 tanks of fuel with injector cleaner run through it, known good EGR valve installed.

Can't check the codes because its a OBD 1.5 type system. Maintenance manual points to TPS, MAP, Coolant Temp or EGR Valve. The sensors are the input for EGR.

When Idle air control valve is disconnected erratic idle goes away. I'm thinking TPS but don't want to just throw parts at it. Any suggestions?

[GP1138]

The IAC comment makes me think that's the culprit. Use some carb cleaner and clean it real good. I believe some members have soaked it in gasoline, but I used water myself and cleaned it real good, it fixes idle issues.

As for the cruise, I'm not sure if the IAC has anything to do with cruise control, so I'll keep my mouth shut on that.

[jb88ci]

Sorry, not cruise control but when the tranny kicks down into OD...i'm an aircraft mechanic....wrong terminology.

[3pt1lumina]

Hmm, bucking while driving leads me to believe bad intake gaskets? Dad's 97 Lumina did the same thing.

[Crazy K]

I had a similar issue in a 3.1.
The cause was a bad engine temperature sensor(the sensor for the computer) it was giving an erratic signal. The computer regulates the fuel mixture as well as triggers the fan relays based on the value the sensor returns. A cold engine needs to run richer that a hot engine... my symptoms occurred when the engine was warm. The engine would sputter and surge running rich, and the fans wouldn't turn on even as the sputting motors temperature started to climb (per the gauge, it was 95*F outside). No check engine light lit up either.

Try replacing that, it should be pretty cheap, afterall :) - Ken

[jb88ci]

Engine is 'overcooling' needle hardly moves when driving but temp will come halfway up the range when idling, waiting at a drive thru or in traffic, before the fan kicks on....just might be teh culprit.

[Crazy K]

hmm... what you just described sounds like a thermostat! try changing that!
However...
I have seen many sensors that have lost their calibration with age as well... If in doubt, there are also two temperature sensors, the second for the light/gauge. You might get those all changed in the same shot as each of those thread into a coolant passage. AND seal them with liquid teflon!

Both sensors, a themostat and teflon sealant (try advanced, i thing autozone doesn't carry liquid teflon) will run around $45 total.

[michaelvettel]

Looks like it needed a quick fix, some cars is just way to overrated to fix of some minor parts is the major issue to keep the car running.
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Idle Control Valve (http://partstrain.com/ShopbyDepartment/Idle_Control_Valve)

[WhatTheFehl]

Holy necrobump batman!