Fault code P0638

[Landy Andy]

does the engine run ok, then you rev it, then, when it returns to tick over it surges???

 

[tidewatcher]

When you first start it the tickover is smooth until the engine gets slightly warm if it starts hunting on tick over you can rev it and sometimes it will drop back to a smooth tickover but then it will slowly start to hunt again. Drives well under load and acceleration but again when it drops back to tick over it will hunt over fifty percent of the time. Hoping a change of the dpf controller and some dpf cleaner will give it a hand.

 

[tidewatcher]

Changed the dpf control valve and checked there was vacuum getting to it when the engine is running. Engine starts and is fine for two or three minutes then starts to hunt on tick over, if you slowly open the throttle it chugs until you reach about 1500 rpm. Have yet to give her a good run and hopefully early next week can do ten to fifteen miles at 2500 to 3000 rpm if that sounds about right. Really do want to get this sorted now as not happy about long trips until she sounds right. Sorry to keep popping up but kind of loosing confidence in the van at the moment.

 

[Landy Andy]

Changed the dpf control valve and checked there was vacuum getting to it when the engine is running. Engine starts and is fine for two or three minutes then starts to hunt on tick over, if you slowly open the throttle it chugs until you reach about 1500 rpm. Have yet to give her a good run and hopefully early next week can do ten to fifteen miles at 2500 to 3000 rpm if that sounds about right. Really do want to get this sorted now as not happy about long trips until she sounds right. Sorry to keep popping up but kind of loosing confidence in the van at the moment.

Don’t worry about keeping us informed. That’s what we (me) want.

You did check your EGR whilst TB off? Did you apply vacuum and test EGR again?

You say the DPF control valve is that what you mean?

 

[BillyBear]

About a year ago I had the exact issues you describe. The local mechanic had a look and told me he had reset the throttle parameters and the motorhome has been fine since then but he also said if he had to point a finger it would be the EGR valve messing about.

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[Raul]

I would remove and clean the egr of the engine, ( Mr muscle oven foam cleaner) and the pipe that feeds the air to the intake, from EGR. Your manifold is a little choked by soot. No way any additives will help you with that. Proper of the engine manifold of, degreaser and sweat.
I had in the past a vx combo hunting to the point that the engine vibration destroyed the rear engine mount. Upon lots of inspection, cleaning this and that, scanning all parameters ok, I took the air valve ( throttle body) off to clean, revealing the sooted choked manifold. The only thing that sorted the hunting and improved power, was to take the bull by the horns: remove the manifold, soak in a container with petrol, then brake fluid to help cleaning it and finally mr muscle to give it a shine like new. My wife drove it after I finished with it, her words: it goes like shit of a shovel now at roundabouts when you need it most.
Do not try to clean it in situ, you will ram lots of solid soot on top of the valves down the air ways; really bad and a head out to rectify.

 

[tidewatcher]

Don’t worry about keeping us informed. That’s what we (me) want.

You did check your EGR whilst TB off? Did you apply vacuum and test EGR again?

You say the DPF control valve is that what you mean?

While the throttle body was off I tested the egr valve using a vacuum gauge which showed no vacuum leaks. I changed the electro pneumatic controller which sits above the engine centrally and has the two vacuum pipes, one from the servo vacuum side and one to the egr valve itself. I have checked there is a vacuum reaching it and also that the pipe to the egr valve is not blocked.
The odd thing is that when first starting the engine the tick over is as before, about 800 rpm and steady. After a few minutes it suddenly starts to hunt and then if you slowly increase the revs it has a hesitation but if you blip the throttle it is clean. Driving the van will pull cleanly if you floor the throttle even from quite low revs in a higher gear putting load on.
Never had a dpf fault code, the only one that came up was the P0638 throttle body.

 

[Pugsy]

Changed the dpf control valve and checked there was vacuum getting to it when the engine is running. Engine starts and is fine for two or three minutes then starts to hunt on tick over, if you slowly open the throttle it chugs until you reach about 1500 rpm. Have yet to give her a good run and hopefully early next week can do ten to fifteen miles at 2500 to 3000 rpm if that sounds about right. Really do want to get this sorted now as not happy about long trips until she sounds right. Sorry to keep popping up but kind of loosing confidence in the van at the moment.

Keep us updated ,I feel your pain as i am having similar issues at the moment and it sounds like plenty people have had the same. Keep your chin up it will get sorted it s all good information for us
and as usual loads of info and help from the funsters . I have someone coming to go over mine in a week or so will see what happens.
Cheers Cris .

 

[tidewatcher]

Todays update! Wondered if the new throttle body needed pairing with the management system so a googling I did go. As usual you can pick your answer, however there were a number of sensible looking posts which suggested it should be and they gave two ways of achieving it. First was the good old removed the starter battery earth strap for twenty minutes and the other was to turn on the ignition for two minutes but not start the engine a few times. Took the easy option of suggestion number two. Then started the van and maybe a slight improvement on the tickover but headed out and gave the van a fairly heavy pasting but only for about five miles as time was pressing. Some white smoke from the exhaust and the engine did get well up to temperature. The result was an improvement though not yet perfect. Very little sign of lumpy tick over, engine revved freely and pulled cleanly and well. No management light on.
Sooo…..
Hope to give her a good ten mile plus run up the motorway now it seems it will keep going, as I said not perfect but a big improvement which makes me think the fault is (was) ninety per cent EGR and ten percent confusion in the management system.
We will see. Thinking of selling the film rights as I reckon it would make a good mini series on Dave.

 

[Sue and Rick]

Have you looked at the actual and expected flow rates of the air mass sensor?
If this is faulty the revs will go up and down (hunting) on tickover.

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[tidewatcher]

How can I do that?

 

[Sue and Rick]

How can I do that?

You need the proper software. Is your van a ducato or peugeot?
Some other software will read the values. I have a peugeot and the cloned manufactures software.
A cheap £10 reader does my wifes Mokka readings. Select live data on the reader

 

[tidewatcher]

Thanks will check my reader and have a look.

 

[Sue and Rick]

Thanks will check my reader and have a look.

The code also suggest possible throttle (pedal) malfunction. You can test the position of the pedal using some software to rule that one out.

 

[Landy Andy]

A failed/sticking EGR, a gummed up MAP sensor, can also cause incorrect MAF sensor readings.

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[tidewatcher]

A failed/sticking EGR, a gummed up MAP sensor, can also cause incorrect MAF sensor readings.

Will run diagnostics tomorrow using a garage friends better kit. Still think it’s a sticking egr but hoping a thrash with a good dose of cleaner helps. In honesty with the faulty throttle body I was driving very gently to get home from France which wouldn’t have helped.

 

[Landy Andy]

Will run diagnostics tomorrow using a garage friends better kit. Still think it’s a sticking egr but hoping a thrash with a good dose of cleaner helps. In honesty with the faulty throttle body I was driving very gently to get home from France which wouldn’t have helped.

A good few drives will be a good start in your diagnostics as they can require a few drive cycles so set its parameters.

Incorrect MAF readings was one of the indicators of my failed (open) EGR. No warning lights, just incorrect readings.

 

[Sue and Rick]

I found this

In addition, after fitting a new solenoid or throttle body it is advisable
to run a procedure using a diagnostic device 'Re-learn self-learned functions' so that new items can be recognised and adjustments that have been made automatically will be reset.

 

[tidewatcher]

I saw that and also the one which suggested turning ignition on for two minutes but not starting the engine for a few times which I did. The alternative was disconnect the battery for twenty minutes which I assume clears the memory on the management system so it sets off afresh as they say. Plan to give it a few good drives and see if it continues improving and if not will then head down the more advanced OBD path. Every days a school day.