PontiacBonnevilleClub.com

1990 3.8.

Today i was driving 50kmh with steady light trhottle. Then engine started to rev 1500 and 2500 up and down and car moved like kangaroo. When i stopped first time, idle was good and car was fine at moment. Checked fault codes, none.

Couple kilometers and same up and down. In red lights d and brake on idle were 500-0 up down and then died.

Got it away with extra pedal kicking. It was misfiring and banging like hell. Hood up and checked all good. When i gived gas on it it banged on air filter box.

Plugged maf off and same problem. Couple restarts and runned fine on idle. Then tried to drive across parking lot and same problem again. Up down revs in driving situation and very poor idle or stall.


Battery + and - off for while. Car started fine and worked next 500km what i drive.


What is this? Very bad because no fault code and it goed away like nothing.

I would start with cleaning the MAF and Idle Air Control valve.

Maf is quite new. And car works without maf i have tried it before because i had couple bad mafs.

So when i plugged maf off, it didnt change poor behavior

I have now tunerpro and connection with it.

Maf is 6g on idle and increases when i press throttle. What are normal values for maf?

oh no, not you again....lol

do you smell gas from plenum? I would check the fuel pressure regulator - might be bad and sucking gas into manifold causing your miss and bang.

how long since plugs and wires were done?

it would also be a good idea to clean the throttlebody butterfly valve - may not be closing properly

if you got a decent scantool, you can check the throttle position and check if it responds to the opening and clossing of the butterfly.

so I assume you passed your emission test.

Checked all those and they are fine. Next i check injectors.

Car fuel consumption varys to 8liter 100km to 11liters 100km with same route and driving style.

Also bad fuelcut etc is coming in 5000rpm with full throttle. Not all the time... Car bangs and revs drop to 3000rpm.

That fuel consumption makes me angry.


And yes i have tuner pro rt and aldl cable so all hints to what look are welcome

Basic values were okay when i checked cold engine to hot and 15minutes then.

I dont have working battery on my laptop so road test isnt possible

LTFTs hovering around 128 when you scan it?

Can you get a vacuum gauge on it to see how much it's pulling at idle?

I check vacuum soon.





Here values in idle

Values at just under 2000rpm, car in park

So your BLM (LTFT) is the learned adjustment to the fueling. It's is a little rich at idle (124) and more so with no load in park at 2k (120). 128 is perfect, lower is rich and higher is lean. The Fine Fuel Correction (STFT) is the short term correction and only really gives you an idea of how the BLM will change.

I honestly don't think it's that far off to be an issue. I would be curious to see if you have a vacuum leak but the fueling is suggesting no.

Couple times high consumption has normalized when i reseted ecm (battery + - off for 15min)

But i try tomorrow check vacuum.

I know this car can do better than 10liter 100km on highway.

Maf readings are ok?

At warm engine, iac steps were couple times -20 +20 and idle dropped and go back normal but i didnt see nothing values change. Just iac steps.

Vacuum steady 19 in-hg at idling engine /normal opetarion temp.

Decreased smooth up and back when pressed throttle.

The Vacuum seems good also.

This is really two possibly related issues.

-The jumping idle which I still think could have something to do with a sticking/faulty IAC valve stepper motor. Unless your O2 or MAF is grounding out somewhere causing the IAC to go crazy. Your intake air temps seem fine too.

-The MPG issue, I'm wondering if maybe your torque converter isn't locking-up?

100km/10l is like 23MPG. It's not the 26 MPG is was rated at highway but it's not catastrophic failure bad.

TCC is working and revs are low.

This is my second 3.8 car. Even highway drive + little bit city and mpg is that 26 or better.

Now its not gonna get it even highway 50mph steady drive.

It wont swing idle anymore. It drops (you hear it) but just wont see it on rpm needle. Not every run or even week. Maf fixed that humping idle which was problem in spring.


Even winter -25celcius mixed drive it was like 22mpg.

Car starts fine hot and cold

Have the O2 sensor and plugs been changed recently?

The only thing that looks odd to me is the throttle position sensor voltage looks slightly low, like the adjustment is off. I thought I recall that with the throttle closed it should be adjusted to 0.45v. But it's been a while.

4-6g/s at idle seems normal, I think ~150g/s at WOT at redline is the upper end.

You can check the O2 sensor by graphing it's output during a drive. The result should be a mostly regular, yet very excited pattern while cruising; I don't think its a big factor during WOT. If it looks lazy, or slow to cross back and forth or hangs/flatlines during cruising then the O2 sensor needs to be replaced.

02 sensor is not new, plugs are max 10k miles old like wires.

Car is not lazy but that 5000rpm thing bothers me. Because my language i cant find correct term. I try took a video and you see what it does.

What tps should read full throttle if i try it engine off, poer on?

Here is new results: car not running, throttle full, Tps 4.06volts. 0.45volts are in 1600rpm when car runs



Engine temp about 100f and then something happened. Before that fuel trims were 128/128. Then 114/132. Target afr ratio was 10seconds on 13.7. Idle was heavier then.

Now i have video what car does in acceleration and idle. I have aldl connected on idle when car sputters.

https://aijaa.com/AlMOQK idle poor running with tuner pro on

https://aijaa.com/hOUFp1 sputtering was mild. Its usually worser

Tps had ellipse screw holes so i adjusted it. Now 0.45v on idle (no gas) and about 4.5 full throttle. Nothing changed.

Injectors, ecm and o2 sensor are only things that i havent changed or checked :D

you have a scantool that pulls o2 volts so diagnose the sensor - not that hard, then check injectors