2003 SSEi rough idle but fine under throttle

[rynmcdonald]

Albeit I am going to put a Series III in this car, I would like things to work properly with the transition and hope that this problem doesn't migrate to the series iii engine. The previous owner said he put new heads on it and I see he did.

I ran a compression test and got roughly 175+ psi per cylinder on all. I see no vacuum lines disconnected. Tried putting the coil packs and ICM from my series iii GTP on it but that didn't help. It has new injectors on it according to previous owner. When I checked the plugs, the front plugs looked like they were fuel fouled. The rear plugs were burning less rich. I am leaning towards getting another O2 sensor since everything else checks out. If there's anything I may have missed, please let me know.

Thank you.

[MKMike]

Since the PO changed the heads, maybe there are some fuel injector o rings that split.
That's the only way I could see one bank being much less rich than the other.
Common trouble spots are the vacuum T under the SC snout ,a broken connector at the MAP sensor,splits in the corrugated line to the EGR, high fuel pressure from a leaking fuel pressure regulator, and dirty or failing MAF sensor.
(If it is a bad MAF get an OE from the junkyard or a new Hitachi since they made the OE sensor.)
Also look at fuel trims and check for codes.
If LTFT and STFT are high positives at idle but holding rpms at 3k for 30 seconds brings them to normal, you have a vacuum leak.
Good fuel trim article http://www.easterncatalytic.com/educati ... stic-tool/

[rynmcdonald]

Since the PO changed the heads, maybe there are some fuel injector o rings that split.
That's the only way I could see one bank being much less rich than the other.
Common trouble spots are the vacuum T under the SC snout ,a broken connector at the MAP sensor,splits in the corrugated line to the EGR, high fuel pressure from a leaking fuel pressure regulator, and dirty or failing MAF sensor.
(If it is a bad MAF get an OE from the junkyard or a new Hitachi since they made the OE sensor.)
Also look at fuel trims and check for codes.
If LTFT and STFT are high positives at idle but holding rpms at 3k for 30 seconds brings them to normal, you have a vacuum leak.
Good fuel trim article http://www.easterncatalytic.com/educati ... stic-tool/

I don't have a tech 2 scan tool for that. Just a basic LCD handheld. Would that still work?

[MKMike]

It will if it tells you live data as well as codes.

[rynmcdonald]

Not sure if it gives live data.

[MKMike]

Not sure if it gives live data.

Then there's one way to find out....
Hook it up and see if you can read the short term fuel trim and long term fuel trim

[rynmcdonald]

The car has sat for a while because the transmission failed. Could that be a contributing factor as to why it's running like it is?

[rynmcdonald]

Found a missing bolt by front of supercharger. Likely this is cause?? Opinions on this?

UPDATE

Wasn't the cause. I did unplug the MAF and nothing changed and I am wondering if it would cause a change in engine idle. Please advise

[MKMike]

If you have a second Bonneville, why don't you just swap over the known good MAF and see?
Any fuel trim readings? They may be shown as STFT and LTFT.

[MKMike]

The car has sat for a while because the transmission failed. Could that be a contributing factor as to why it's running like it is?

If you're running on the old fuel, which may have accumulated water and lost octane, sure..
Try adding some Techron Concentrate to the tank, if the gas is fresh.
Add some gas line antifreeze and some fresh gas , if the gas is old.
I'd check/change the fuel filter and check the fuel pressure, too.
Also look and see if the PCV is gummed up and make sure there is an o ring and a good seal on the PCV cover plate.
The cover is on the supercharger.
Since the PO was careless enough to leave a bolt off of the intake, it males me wonder if he was careful enough torqueing down the LIM bolts to secure/seal the LIM gaskets.
Check the MAF readings at idle. The reading should be steady.
Tap on the MAF and see if the MAF readings change.
My cars read about 5.5 grams per second at idle

[rynmcdonald]

Letting heet run through it now. Will see about putting fresh 93 in it tomorrow with a fuel filter. I have also swapped MAP and MAF with no changes. Checked consistency of injectors firing and they look good so I don't know what else could cause this short of the upstream O2. Will have a code reader on it soon and let you know what I find. It seems to be isolated to one cylinder or could be random on different cylinders. Crank or cam sensor? Won't know until code reader gets here.

[rynmcdonald]

I have code P0300 after running a scan tool on it

[redzmonte]

P0300 is a generic multiple misfire code. I would have someone scan it for miss by cylinder if yours doesn't do by cylinder. that will narrow it down to what cylinder and then you can start diagnosing the miss, it could be a bad plug, bad wire, bad coil, Ignition module, injector (Bad or plugged), vac leak (best to smoke the engine for leaks), egr causing problems, many things.

hope this helps.
Shane

[rynmcdonald]

O2 S1 B1 Volts are between 0.43 & 0.45. STFT Is 99.2% B1 S2 (that good??) MAP IS 10.9 inHg at idle. Spark advance is 22° at idle. MAF is 0.8 at idle. TPS is 0.4% at idle. Those are live parameters. I don't have a fancy scanner but I can borrow one. Will post again if I can borrow it.

[96 SSEi]

O2 S1 B1 Volts are between 0.43 & 0.45. STFT Is 99.2% B1 S2 (that good??) MAP IS 10.9 inHg at idle. Spark advance is 22° at idle.

hi, no your STFT is not good at all - so these reading are at idle at about 900rpm? your spark advance is way too high compared to my 2000 SSEi -
I have a pesky vacuum leak and my stft at idle is about 15-20% and SA is at 0.

you have to take the fuel trim readings at idle and at 3000rpm to get data for vacuum leak diagnosis.

[MKMike]

O2 S1 B1 Volts are between 0.43 & 0.45. STFT Is 99.2% B1 S2 (that good??) MAP IS 10.9 inHg at idle. Spark advance is 22° at idle. MAF is 0.8 at idle. TPS is 0.4% at idle. Those are live parameters. I don't have a fancy scanner but I can borrow one. Will post again if I can borrow it.

O2 sensor #1 should be rapidly alternating from lean to rich, not reading a rather steady number
STFT if 99% is way off; should be between -10 and 10% --maybe your STFT is actually 9.92%?
you omitted the O2 downstream sensor, which should be a rather steady reading
MAP readings in inches of mercury are unfamiliar to me
Spark advance of 22 degrees is fine
MAF should be 3-6 kPa

[sseilmnop]

Vacuum leaks cause misfires at idle. You say you don't have leaks, does that mean you have replaced the rubber ends on all the vacuum hoses? If your still running the original they are all leaking a little. If you pull them off to check and put them back on they are leaking more since they are old an brittle. Also the flex metal tube from the lower intake manifold to the EGR valve is liable to be cracked causing a vacuum leak.

You can make a cheap smoke checker with a paint can, 12 volt tire air pump, cardboard and and some vacuum tubing. Essentially burn brown cardboard in a paint can and put the lid on and pump smoke into your intake. You tube has a bunch of videos where they build your own. You don't need mineral oil just burn brown card board.

Once you are positive you don't have vacuum leaks i would swap out the idle air control valve on the throttle body. If you idle isn't corrrtect but your not getting misfires this is likely.

Misfires under power/heavy acceleration are typically coil, wires, plugs, ignition parts.......etc...

Hope that helps!