Continuing Rough Idle Saga

[rmoconnor41]

Afternoon,

The vehicle is a 1999. 2.8.

For some time it has had a rough idle when cold. The revs swing between 800-400 until the vehicle is warm. Then the idle is very steady.

It is always throwing trim bank error codes . P0170 and P0173 Fuel trim bank 2 and 1 control limit.

MAF is newish
No air leaks. Thoroughly tested by the shed.
VANOS rebuilt
DISA and ICV checked.
Post CAT O2 sensors replaced.
Smog pump was removed and blanked off.
It threw a thermostat code on the shed's advanced code reader so that was replaced last week.

I am running out of things to check or replace.

Any thoughts?

Thanks

 

[t-tony]

Cam position sensors would be my guess. They don't always throw codes/put EML on.

Tony.

 

[AntStark]

@t-tony what about plugs or coil packs? It literally does it only when cold and then when warm it runs really nicely. Assume it would have a constant issue if either of those ?

 

[t-tony]

Try cleaning the throttle body and also the idle control valve.

Tony.

 

[AntStark]

ICV was done by @Lee earlier in the year..breaking the ‘how fast can I get an ICV out” record by some margin. Rattles like a baby’s toy. Throttle body worth a look.

 

[NZ00Z3]

Why does the rough idle only happen when the engine is cold? That's because the engine control is on open loop when the engine is cold and then goes to closed loop when the engine is hot.

The only main sensor running in open loop is the MAF. As you have checked and fixed any vacuum leaks, try unplugging the MAF and doing a cold start. See if that fixes or improves the problem.

 

[rmoconnor41]

Why does the rough idle only happen when the engine is cold? That's because the engine control is on open loop when the engine is cold and then goes to closed loop when the engine is hot.

The only main sensor running in open loop is the MAF. As you have checked and fixed any vacuum leaks, try unplugging the MAF and doing a cold start. See if that fixes or improves the problem.

Unfortunately I recently had the chance to try a new MAF. It made no difference.

 

[rmoconnor41]

Cam position sensors would be my guess. They don't always throw codes/put EML on.

Tony.

Cam position sensors would be my guess. They don't always throw codes/put EML on.

Tony.

Thanks. Both of them?

 

[rmoconnor41]

Cam position sensors would be my guess. They don't always throw codes/put EML on.

Tony.

What are your thoughts on 02 sensors? The post CAT ones were replaced this summer.

 

[rmoconnor41]

Try cleaning the throttle body and also the idle control valve.

Tony.

One other thing. The smog pump was "enthusuiastically" removed one day and the blanking plate fitted. Is there anything leak wise I may have missed from its enthusiastic removal?

 

[AntStark]

One other thing. The smog pump was "enthusuiastically" removed one day and the blanking plate fitted. Is there anything leak wise I may have missed from its enthusiastic removal?

I think it would have shown up on the various smoke tests. We can have another go but I think you are probably air tight now.

 

[t-tony]

One other thing. The smog pump was "enthusuiastically" removed one day and the blanking plate fitted. Is there anything leak wise I may have missed from its enthusiastic removal?

There would be a small vacuum pipe to the valve you removed. It needs to be blocked off or you will have a vacuum leak. IIRC it comes from the rear of the inlet manifold. If there is no vacuum draw on the pipe when the motor is running, then it is possibly already leaking.

Tony.

 

[t-tony]

Thanks. Both of them?

More likely than not, the inlet cam sensor.

Tony.

 

[Duncodin]

Mine is a 4 cylinder. I have the exact same problem.

Car starts first turn of the key but, to me, it feels like it's only running on 3 cylinders.

Idles rough like that for maybe 2 minutes and then suddenly it'll run smooth.

I must confess it doesn't worry me much. By the time I've closed the garage door and buckled up my seat belt it's running sweet and off I go.

I just put it down to a bad spark plug, weak spark, that will sort itself out next time I service it. If it doesn't then I'll scratch my head and think of something else.

 

[rmoconnor41]

I think it would have shown up on the various smoke tests. We can have another go but I think you are probably air tight now.

Maybe the 2 O2 sensors pre cat need changing. The rear ones were done. Maybe the upstream cam sensor. The cam and one O2 looks straightforward one O2 looks a bit fiddly.

 

[rmoconnor41]

Unfortunately I recently had the chance to try a new MAF. It made no difference.

MAF on and off the car runs the same

 

[ChrisD]

Afternoon,

The vehicle is a 1999. 2.8.

For some time it has had a rough idle when cold. The revs swing between 800-400 until the vehicle is warm. Then the idle is very steady.

It is always throwing trim bank error codes . P0170 and P0173 Fuel trim bank 2 and 1 control limit.

MAF is newish
No air leaks. Thoroughly tested by the shed.
VANOS rebuilt
DISA and ICV checked.
Post CAT O2 sensors replaced.
Smog pump was removed and blanked off.
It threw a thermostat code on the shed's advanced code reader so that was replaced last week.

I am running out of things to check or replace.

Any thoughts?

Thanks

Are your fuel trims indicating rich or lean? Knowing this will give you the direction where to look next. Sorry to say, diagnostics are often time consuming and frustrating but ultimately satisfying when finally resolved. Remember, your engine has three simple requirements: fuel, air and spark. There's still a lot of things that need to be checked (and re-checked).

Also, running the vehicle for long periods in this condition can damage the catalyst - sorry again.

 

[rmoconnor41]

Are your fuel trims indicating rich or lean? Knowing this will give you the direction where to look next. Sorry to say, diagnostics are often time consuming and frustrating but ultimately satisfying when finally resolved. Remember, your engine has three simple requirements: fuel, air and spark. There's still a lot of things that need to be checked (and re-checked).

Also, running the vehicle for long periods in this condition can damage the catalyst - sorry again.

Thanks I will run it and perhaps you could let me have your thoughts thanks Richard

 

[rmoconnor41]

Thanks. Both of them?

I have had a look online at cam sensor The price and range of brands is huge. Is the original made by Siemens.
12141703221

 

[rmoconnor41]

I have had a look online at cam sensor The price and range of brands is huge. Is the original made by Siemens?
12141703221