Rough running

I have a 2000 P38 V8 4.6 running on petrol/LPG. She has had a rough running problem and think I've gone down a couple of blind alleys.

The engine starts no problem but seems to hunt for a steady idle. If driven the hunting continues to the point of sometimes stalling if stopped at lights etc. However the "stall" happens even when driving - I feel the loss of power momentarily but the motion of the car keeps it running until it picks up again (quickly). Doesn't feel like a mis-fire but like a stalled engine

This was intermittent, ie I could go for a run like this but after a short distance switch off and on again and she ran beautifully. Smooth, no hunting and plenty of power.

The intermittent nature lead me to an electrical fault so have checked fuses, relays, fuse boxes, battery & alternator and connections. All good.
Have replaced MAF & O2 sensors which seemed to make a difference for a while but then back to fault.

Have checked obvious on ignition - no arcing and appears reasonable spark (she ran on all 8 smoothly). No obvious leaks, tired hoses etc.

Problem is same irrespective of running on LPG or petrol.

Don't have easy access to diagnostics (will mean a day of work to take it to nearest indie) and not really confident driving 20/30 miles with it like this.

I get both gearbox fault and traction fault messages but not always. On start up I sometimes don't but it comes as soon as I start driving. When she runs well the gearbox fault has cleared. It also seems the problem is worse between 1500 - 2000 rpm (but may just be me).

Any thoughts (apart from the obvious of plug in diagnostics )

Sorry to be long winded.

could be coil pack . If your gas is not set up correct then your fuel trims will be all over the place. You can check this with a cheap ODB II plug in diagnostics (£20-30) and also read/clear any faults. Could be your idle control valve. Gearbox faults only come up when your output volts drop or bad battery , or theres not enough power generated ,when theres not a genuine fault on the gearbox. Did you get a genuine maf as the cheap ones dont work, as i found out.

Take the idle control valve off and see if the spindle inside rotates freely. There may be a little soot in there . I would spray a little wd40 in there and quickly twist it like a bike throttle. The spindle should rotate freely whilst doing this

Willos

Thanks for the quick reply. It's not a genuine MAF but, I ran for a while with it disconnected and it was worse. Might be worth another try. Coil pack I had discounted because it di run well at times (the onboard computer showed circa 19 mpg on dual carriageway!!) but could be sign of starting to fail?
Any recommendation for cheap OBD ii - i didn't think they could clear fault codes?

Gearbox message is what sent me down electrical fault route initially. Just hoping it isn't gearbox itself.

Just look on ebay. Buy one in uk as you dont want to be waiting for one from china.
item no 151692333815 is the sort of thing your looking for or just search for obd II scanner and all sorts pop up. The bluetooth plug in is good if you have an android phone or laptop with bluetooth.
When my gearbox light came up the battery was failing. Check volts across the battery should be around 14v when running. Check your earth leads as this might be the case on the alternator block and at the rear of bank one (drivers side) attached to the rear of the cylinder head.
The scanner will only delete fault codes from the engine. They wont go into ABS/grearbox etc. It will give live readouts of O2 and temps, spark angle BDC , and fuel trims. Saved me a fortune

Again thanks, scanner ordered. Will give IACV a clean up whilst i await postie

Have already checked voltages and earth leads, 14.4 if I remember & 12.8 not running.

Trevt said:

Again thanks, scanner ordered. Will give IACV a clean up whilst i await postie

Have already checked voltages and earth leads, 14.4 if I remember & 12.8 not running.

Click to expand...

14.5 volts on the 4.6 at 2K rpm 12.5 to 12.8 after standing overnight

Willos - you may just have proved me blind/stupid/an eejit. Delete whichever you choose
Taken off the IACV and, because the LPG is right above it, took it completely away with the hoses. underneath the air inlet hose there's a split in the housing where the pipe connects. Cue a search for a replacement.
Saying that the IACV seems very loose and free but gave it a quick clean out with carb cleaner anyway.

Datatek - those voltages ring a bell. I think it was one of your previous posts I took as my guideline when I checked them. But thank you

Sealed the air leak, but no joy.

Sat with engine running tonight after refitting. ran at fast idle ~1500 rpm and dropped (as if an old fashioned choke was being taken off), almost stalled but picked up to 1500 again. dropped down to circa 750 rpm once warmed up.
But all the time almost stalling like the choke analogy
On the gearbox fault cleared on restart but as soon as I revved engine up pops gearbox fault and I lost the "P" in display.
Was going to re-check battery voltage but couldn't hold revs at 2000 - they fluctuate all by themselves

Hopefully code reader will arrive tomorrow

Had some rough running, hesitation etc on both the P38's a couple of weeks ago.. one was intermittant for a few month. both were throwing error codes on the 02 sensor.

1 P38 - changed the O2 sensors cleaned the MAF better, but still off. Changed the spark plugs to NGK platinum.. goes like a scalded cat again.

2 P38 changed the plugs, changed the O2 sensors better but still rough. swapped the MAF from (1) went like a scalded cat again... so cleaned the MAF and all is good in the world with both..

O2 Sensors, MAF and plugs are the first stop... On LPG you will go through plugs more often due to the nature of LPG . it seems to be recommended for 15k on a plug change when LPG is in use.

Okey dokey, scanner has arrived and 4 fault codes stored:

- P1667 & P1551 - a quick suggests these are LR specific and to do with alarm settings? I may be wrong but discounting these for the moment, if there was a fault unlikely to start at all?

- P0505 (Idle Air Control System) & P1514 (Neutral Drive Load Fault L) - again a quick search suggests these are related and both point towards IAC. So thinking will replace IACV and see what happens.

But first have cleared all codes and will take for a local run later to see what reappears. Briefly drove up and down driveway with no codes reappearing. But the gearbox fault message did come back on.......maybe need to recheck battery voltages once steady running is achieved.

Any thoughts or seen these codes before?

P1551 is ICV open circuit (nothing to do with alarm!). I'd suggest that your idea of replacing the idle control valve is a good place to start. Or, rather, check the wiring to it first, then replace.

Thanks for the correction.

Just been out for a 20 mile round trip dropping off and picking up a few things. Ran sweetly

So IACV seems to be culprit, or rather the cracked air hose to it. No new codes

Will run for a couple of days and see what happens.......

So been running for weekend after clearing codes. A couple keep reappearing and set off all the symptoms:
p0172 system too rich or alternatively either bank 1 or 2 rich;
p0123 throttle/peddle position/switch A circuit high input
p0103 Mass or Volume air flow circuit high input

The last two seem to be the culprits?

Will order a new MAF (bosch) as a starter and then try on the throttle control?

Does my logic make sense?

Cheers

I think my code reader shows live throttle position I changed mine and same problems
Check you've live date from the maf to make sure it's duff

Willos

Thanks, I'm using a bluetooth adaptor with Torque on my mobile. Figured out how to get a live data stream this evening but unfortunately not how to record it and email to my pc!
However for the brief while I could see a value against the MAF (10.3 g/hr ?) at idle with an increase when revs went up.

A better call might be worth cleaning out throttle body and ordering up a new potentiometer. I can check wires for dame when I fit it.

If that doesn't work I'll try the MAF. I did run for a while with the MAF disconnected and it was rougher which would seem to suggest it's doing something right.

Whole new world that scanner