I recently purchased a R53 project. It is a 2004 with ~200k miles. The symptoms were that it would start but barely stay running without spraying starting fluid in the throttle body or around the vacuum leaks. It has a lot of recent maintenance, likely to try to fix this issue.

I fixed all the vacuum leaks (bypass valve, supercharger intake duct gasket, sealed the seams in the inlet duct) and verified with a smoke tester that there are no other vacuum leaks.

It will start and idle fine and rev for about 4-5 seconds. Then it will drop down to a lumpy idle between 400-600 rpm and the accelerator pedal has no affect. I have INPA loaded on a laptop and verified the throttle position at the pedal and the throttle body is responding as it should.

It has codes for both O2 sensor heater circuits (S1 short to ground, S2 no signal), fuse 3 for the O2 circuit is good. The voltage for the precat 02 sensor is 0.8-0.9V when it starts and runs well then it drops to around 0.1V when it runs poorly. It does this every time, no matter what the temp is, I can keep it running poorly long enough to get the coolant temp up to normal operating range but it still does the same thing. If I disconnect the precat O2 sensor there is no change.

The third code is for low idle.


Any ideas on what to look for next?

Fuel pressure is good at the rail (~55 key on, engine off and ~40psi when it is running well, when it starts to die the pressure goes back up to ~55psi).

 

0.1 V from the pre-cat O2 sensor indicates that it's running very lean. BUT, since the heater circuit on the sensor is reading faulty that means the voltage output from the sensor cannot be trusted.
Step one would be to replace the sensor and clear the codes. This might explain why it runs fine for a few seconds. Right after start-up the engine runs in open-loop mode which ignores O2 sensor readings.
If that doesn't solve it then perhaps it's a clogged or faulty fuel injector.

 

If it’s a project car, how old is the gas? My 06 project car would do similar and decided to discard with all the old gas and put in fresh and it started fine.

 

I fixed the o2 heater fault, it was two wires in the harness that were abraded and touching. Now the only fault is the rear o2 no signal.

The previous owner threw a lot of parts at it before giving up about a year and a half ago. Injectors, fuel pump, plugs, wires, coil, etc. I don't know if the fuel filter was changed when the pump was, can the pump be changed without doing the filter too?

There was less than a 1/4 tank of gas in it. I put 5 gallons of fresh gas in yesterday. It seemed to be doing better after I let it run long enough to warm up, it would take throttle but still break up. I shut it off for 10 minutes and it was back to the same thing.

I found the area in the INPA software to temporarily adjust fuel trims. Adjusting the trim up to +1.0 got it to idle smoothly. When I reverted control back it went back down to 400-600rpm and wouldn't take throttle. For some reason fuel trims will not display in INPA for it (or they are just all at 0.0 and the computer isn't adjusting them at all for some reason).

 

Good tip, especially with the added ethanol in gasoline these days. Shelf life is about 3 months and then the quality starts to deteriorate if I recall correctly (for E10).

The error messages you posted show an error in both sensors btw. I had the same error on Bank 1 Sensor 2, which is the post cat O2 sensor. I replaced it with a new one (Magneti Marelli) and needed to clear the error using INPA. The code would not dissappear with Torque Pro app.

 

Wife overheated the engine and I had to do an engine swap. Got everything swapped over and is running exactly as you describe. Starts, lumpy idle, doesn’t respond to throttle. New MAP sensor, crank and cam sensor, still the same. No fault codes showing. Don’t have the advanced tools to check the other things. Scratching my head, about to pull my hair out. Any advice? Also, due pressure steady at 49 psi

 

I'm still working through my issues with no resolution yet. I did find today that the rear o2 sensor fault is because it isn't even the correct sensor. It looked like it was plugged into the connector but the keys on the sensor connector were not right for the vehicle side connector so it wasn't plugged in all the way, the two connectors were just nestled together. I have a correct NTK sensor on order that will be here tomorrow.

Another issue with the rear o2 is the cat is installed backwards. Whoever installed the aftermarket cat into the aftermarket exhaust welded it so the post-cat o2 bung is before the cat. Not sure how good the results will be with both sensors being before the cat and inches from each other but that will at least hopefully clear that code and I can see if that makes any difference.

 

That will give faulty results indeed. You can leave it like that, but then you need to add a O2 spacer, but I would recommend turning it around so it sits as intended.

 

So with the correct rear o2 sensor in there are no more codes. It will go into closed loop when I can keep it running long enough to warm up and idles fine with STFT at +30. I let it run like that for about 30 minutes and LTFT never changed. It will rev a bit and I can drive it slowly but it bucks and dies under too much load. Even in closed loop with the STFT adjusted so it idles well the front O2 is reading 0.00 to 0.01. The rear o2 is around 0.10v. I need to fix the cat orientation and remove the header to weld up any cracks were air could be getting in causing a false lean. I would still think that the computer would be trying to add more fuel with the o2 sensors reading that lean and it wouldn't make it run this poorly.

I have thought about it possibly jumping time but there isn't an easy way to check that. In INPA there are no errors for the cam or crank sensor or engine sync.

 

You may want to replace the Fuel filter (the one at the Fuel pump) it might be so full of sludge that is is not getting the amount of fuel to the rail to keep the engine running at proper idle rate.

Best of Luck.

Motor On!

 

Still no resolution.

I changed the fuel filter (the old one was fairly black). Still the same symptoms. It will start right up, rev to 1500rpm or so and start to settle down into an idle but then stalls. Occasionally it will try to smooth out and idle but can't do it and dies.

 

Mine did this when the fuel pump was going out.

bang on the back seat over the fuel pump...will fix it for a sec. that’s the tell

 

Fuel pump was replaced recently (by previous owner) and fuel pressure is good.

I pulled the plugs and did a compression test. The plugs were all black and sooty, definitely doesn't look like it was running lean. These were also new when the PO threw the parts cannon at it.


Compression from Cyl 1-4:

158
164
156
166



So maybe once it enters closed loop and fuel trims go up it is actually running so rich that it reads lean which is why the o2 sensors are nearly at 0.0v. That is still confusing since that is the only time it idles well except initial start. It will rev fine on initial startup but after a couple seconds it won't take throttle, doesn't matter if it is idling at 1500rpm and then just drops down or if the throttle pedal is pressed and it is revving at 4-5k rpm it will just shut down and not respond.

 

Are the 02 sensors flipped?

 

No, the o2 sensors are plugged in correctly.

 

Resurrecting this from the dead- did you ever sort out this issue? I am having VERY similar problems with me 200k+ mile project.

 

Unfortunately not. I scoped a number of sensors and didn't see anything unusual. Pulled the timing cover and oil pan and the timing marks were spot on. Eventually gave up and moved it to a different type of project.

I did get a used ECM for it but never got around to seeing if I could make it work with the car to find out if that was the issue.

 

I had put non OEM injectors in, same size, allegedly the same spec but they didn't wok, also a non OEM MAF sensor. Learned the hard way to only use OME sensors. Cost more but they did the trick.