Bad sputtering/misfire?

[ak-]

SOLUTION: CAP & ROTOR.

Okay, here I go:

MAF converted m20b25 running well for over a year.

Had a bad idle for a while recently. Stutter below 1000rpm and between 2-3000rpm only, and my rpm's would fall down very slow when letting off the throttle. My TPS also wasn't clicking when engaging the throttle/butterfly so we figured it was that and replaced it.

Everything got 100% better; felt like a new car. I was satisfied.

One hour later into driving:
-I start getting a CEL.
-Sputters the first few seconds when giving it throttle before going normal.
-Exhaust POPS when revmatching/downshifting instead of the usual quiet burbul.

One day later:
-CEL still on.
-Starts up and idles well after 1st start up only.
-Stutters/misfiring completely when applying throttle; just won't "go".
-Misfiring at idle, sounds like a cammed Camaro. blub-blub-blub-blub-blub.
-Smells like gasoline everywhere and more so near the engine bay.


Misc:
Spark plugs are new. (OEM copper)
Fuel filter new.
MAF conversion was done a year ago.
Cap/Rotor done a year ago.
No intake leaks.

I'm confused on what happened since everything was dandy for about an hour of driving and after one day I'm misfiring like a Jihadist with an AK.
Any insight is appreciated.

[ak-]

[jlevie]

What you describe sounds like an engine that is running lean to the point of misfires. The fist things I'd suspect would be intake leaks, a fuel system problem, or in this case the "MAF conversion". Intake leaks are best diagnosed by have a smoke test run on the intake and the fuel system can be tested per the procedures in the Bentley.

[ak-]

Thanks.

The MAF conversion is ruled out since I've had it for over a year now with no problems.
Intake leaks are also ruled out as we thoroughly checked at a shop.

Remembering correctly now, the little rod that goes into the TPS was dripping with oil and I forgot to clean it when putting the other TPS. My friend told me that the seal under the throttle body is done for(maybe this is why the car ran so beautifully for only an hour after switching TPS's) and oil is getting into the sensor causing blow-by, so we are going to try a new throttle body.

I'll update this when finished.

Any other insight is welcome!

[lolcantturn]

[jlevie]

The oil in the intake is from blowby and probably bad valve seals. The throttle plate shaft doesn't have a seal, so oil will seep down. It takes quite a while for oil to get into and ruin the TPS and when it does it will only affect idle and WOT operation. To prolong the life of a new TPS on an aged engine, drill a 3/6" hole in the center of the round section of the bottom of the TPS. That lets the drain out.

The MAF conversion is just as much of a suspect at this point as are intake leaks or a fuel system problem. Rule out the latter two first by the appropriate diagnostics.

[tinkerputzer]

Put it back to stock form so you don't end up troubleshooting yourself in circles.

[ak-]

Put it back to stock form so you don't end up troubleshooting yourself in circles.

We did and got the same results as mentioned. I'm beginning to think it's a coincidence that something else is wrong?

The oil in the intake is from blowby and probably bad valve seals. The throttle plate shaft doesn't have a seal, so oil will seep down. It takes quite a while for oil to get into and ruin the TPS and when it does it will only affect idle and WOT operation. To prolong the life of a new TPS on an aged engine, drill a 3/6" hole in the center of the round section of the bottom of the TPS. That lets the drain out.

The MAF conversion is just as much of a suspect at this point as are intake leaks or a fuel system problem. Rule out the latter two first by the appropriate diagnostics.

Hmmm. I'll try the drain trick.

I'll try switching MAF's to see if one is "dirty" and go on from there. I really don't think I have intake leaks, but I'll try again.

Where can I start with checking the fuel system?
Bad FPR? Pressure? Fuel pump? Clogged injectors?

Is the CPS also a possibility?
My friend noticed that the CPS and plug wires were joined/taped together OEM style, making us think that they could be original(150k+ miles)?

One more thing I'll add is that the car starts fine and idles very well after start up only. I only get bad sputtering when on the throttle under load and not on idle. After driving for a few seconds to a minute is when I get the loopy blub-blub-blub-blub idle/misfiring.


Thank you J.

[tinkerputzer]

If you have a cel you should do a stomp test and see what that tells you.

Also, faulty plug wires will definitely cause a missfire under load. Something to help identify arcing plug wires is while the car is idling, spay them with a mist of water. If they are bad they will start arcing and cause a missfire.

If you don't know when the last time the the cts has been changed it is definitely worthwhile to change.

Best of luck.

[jlevie]

In the stock configuration the CPS wire isn't taped to anything. It, the Cylinder ID, and oil pressure switch wires run in a plastic chase that clips to the front timing cover.

There is a suite of fuel system tests in the Bentley. Run though those and you'll be able to ascertain the health of all parts of the fuel system.

Does the O2 sensor have 100k (or more) on it? If it does replace it. It sort of sounds like the idle is good when the DME is running in open loop mode, but degrades once the engine switches to closed loop mode. A bad O2 sensor can cause that.

[ak-]

If you have a cel you should do a stomp test and see what that tells you.

Also, faulty plug wires will definitely cause a missfire under load. Something to help identify arcing plug wires is while the car is idling, spay them with a mist of water. If they are bad they will start arcing and cause a missfire.

If you don't know when the last time the the cts has been changed it is definitely worthwhile to change.

Best of luck.

My last stomp test was 1222 I think. Not entirely sure if it was 1221 actually, which is the O2 fault code.
I will do the spray test and report back and most likely change the wires any way the following week, thank you!

My CTS is brand new; ~200miles on it.

In the stock configuration the CPS wire isn't taped to anything. It, the Cylinder ID, and oil pressure switch wires run in a plastic chase that clips to the front timing cover.

There is a suite of fuel system tests in the Bentley. Run though those and you'll be able to ascertain the health of all parts of the fuel system.

Does the O2 sensor have 100k (or more) on it? If it does replace it. It sort of sounds like the idle is good when the DME is running in open loop mode, but degrades once the engine switches to closed loop mode. A bad O2 sensor can cause that.

Alright, I will rule out the CPS now then since somebody just told me something similar and that the car wouldn't even really start and/or many other things would be going wrong with a failed CPS, thanks!

Fuel check-up will be next accordingly.

Yea, my O2 does have a bit of miles on it. I will change it this week.


Thank you guys!
I'll update when I get the parts in.

[jlevie]

1221 can caused by a bad O2 sensor, but it and a 1222 code are more commonly the result of an upset in the A/F ratio. As I stated earlier, a smoke test of the intake and the suite of fuel system tests should be the first diagnostics run. If they, or the repairs they indicate, fail to resolve the problem, I'd revert the engine to a known good AFM. That may not solve the problem, but it puts the engine management system into a known state for further diagnostics.

[castros]

AK bring it to the shop on wednesday, and I will check it for free Bahdy!

[IRON-E]

Bad CPS, you'll thank me later.

[ak-]

1221 can caused by a bad O2 sensor, but it and a 1222 code are more commonly the result of an upset in the A/F ratio. As I stated earlier, a smoke test of the intake and the suite of fuel system tests should be the first diagnostics run. If they, or the repairs they indicate, fail to resolve the problem, I'd revert the engine to a known good AFM. That may not solve the problem, but it puts the engine management system into a known state for further diagnostics.

Thank you J. I will do those steps next to see where I'm at.
I really really don't want to revert back to an AFM, as the MAF conversion also had a tune specially made for it and a bunch of wires will have to be pulled and such to put back the AFM along with finding a stock 173 chip.

AK bring it to the shop on wednesday, and I will check it for free Bahdy!

Thank you bahdyy. :p
The new throttle body with TPS didn't do anything :(
Oh, and we had to drill out a new hole in the throttle body since I have a 2-hose charcoal canister thing going into it, not 1 lol.


Thanks again guys