Hi,

On my 1996 e250 I must live with uneven idle. It is almost perfect but not 100% and I can't accept it until it is perfect. Almost everything is new: spark plugs, distributor cap, rotor, cables, all o2 sensors. The engine sounds very healthy mechanically. The idle imperfection isn't rhythmic so I am sure it is not mechanical failure generated. The scanner says the EGR valve doesn't work properly. Until the new part arrives ( Im in Europe...) the line is plugged. Can this cause the small misfires ( this is really small, most people would't takecare of it ) or I must search at other places?

My mechanic says he doesn't like my cat converter, however it doesn't rattles and doesn't seem to be blocked as the engine revs freely and pulls strong.

My mpg isn't perfect: at very careful drive style ( 55-60mls/h) 14.9 mpg with 95 octane, so very good quality fuel. I red it can be 17-18mpg if the engine is in good shape. At 2Dollars/liter it cares too.

Don't hesitate to shoot your ideas, I want to make my van perfect ( I like it very much ).

 

Not sure about the fuel economy, but don't drive yourself crazy over an absolutely perfect idle. I remember my brand new '07 F150 would sometimes vibrate a little at idle, and this wasn't a sign that something was wrong.

 

E150 4.6 1990? 1996 e250? Could help your inquiry to ID which motor?

However, your complaint & story reminds me of TPS symptoms. Ever replaced the Throttle Position Sensor? They have a bad habit of getting iffy at idle.

 

It is a 5.8 engine. Only those parts are new which I listed. So the TPS is original. We looked its resistance with scanner and it was rising continously like it has to be done. We found it OK.

 

Not 100% sure how "it was rising continuously" relates to 'Uneven idle' complaint. Presume you checked TPS resistance throughout it range as throttle is opened?

That's not the issue at idle, where TPS is parked at its end stop & resistance needs to remain stable NOT "rising continuously".

The TPS is rather delicate, low power rheostat, comprised of a cylindrical carbon strip w/tiny copper contact that rotates against it. The contact always parks at idle end, accelerating wear there & any debris tends to accumulate there. As a result the rheostat is most likely to develop problems at its rest position. Vibration can make marginal contact vary upsetting idle.

 

Yes I understand what you explained. If I rev the engine higher it runs also there little more rough than it should, which can sound strange as I never saw another 5.8 running as that van is as rar here as a two stroke Barkas on US streets. But I can identify mechanical originated idle problems and combustion originated problems.

Question: can it be that the ECU switches in a kind of emergency mode if it detects there is some problem with the EGR system?

 

Are you sure that your EGR is plugged correctly?

See EGR Systems - how it works

It explains EGR and there is a part about problems with idle stumbling if any exhaust gas can enter the combustion chamber at idle. If I remember correctly, the EECIV doesn't cause a limp mode but will record a DTC for a non-op EGR. Did you plug the vacuum pipe to the EGR valve also?

 

I didn't plug it, but the mechanic. The last he mentioned I should remove the piece of paper to see what happens. Then I drew my eyebrows a bit as didn't think a normal piece of paper can resist against the hot gases. So I don't know. I am sure they didn't closed the vacuum hose either. I will check. Can an EGR problem lower the mpg result?

 

Yes it can. The EGR not working as it should would cause the engine to think that there's either too much or too little EGR, and therefore the mixture would be off as a result.

 

I will deconnect de battery to erase the CEL and then remove that paper, to see if the failure code comes again. There is an L shaped small rubber tube think as my smal finger, it seems to be very cracked.

 

Today I removed the EGR plug. The EGR vacuum line wasn't plugged by the way. I inspected the EGR it seems to be OK. I don't know why the mechanic told it is leaking. With a motorcycle brake bleeder we produced vacuum just to see if it works and it does perfectly. No sign of imperfect fit of the piston in it, so I put it back and we cancelled the failure code. The way to home was few miles only during this trip the CEL didn't came on but last time it came only after a longer way so I don't say the CEL won't come.

I was informed my my friends father the uneven idle won't come from the EGR as it doesn't work at idle speeds, so there must me something else.

With the OBDII scanner we checked some values, some were interesting:
- coolant temperature was 95Celsius which is quite a lot, but a high value does't make problem theoretically
- the control O2 sensors value was changing too much as the cat wouldn't work efficiently
- the spark advance was after start ( engine was handwarm ) 16 - 18 - maybe 20 and later when it was warm even the 14.5 15 16 which seems to be too much! I don't know how accurate these calculated values are, but if they are then the spark advance must be adjusted. Everywhere I read 10 degrees. The 14 and more seems to be too much as the 6.0L setup with closer gap spark plugs and stronger coil needs 13 - 13.5 so the stock engine shouldn't be adjusted to so early spark, but please correct me if I am not right.

The experienced mechanic also told me he doesn't think there is a problem with the peripheral units like the PCV valve or the idle air control valve ( however for me that valve is suspicious ) for him the injectors are worth to check or at least he would pour an injector cleaner into the tank ( I have never seen any result coming from such wonder liquids ).

What do you think?