Engine not revving properly - Mass Air FLow issue?

[treeman]

My E53 X5 3.0 Diesel 2003 was running fine until I tried to overtake someone and the engine spluttered and power dropped. Although it started, ran and revved up to 2000 rpm fine, anything above that spluttered, as if it hit a rev limiter. On mechanics advice I disconnected the MAF (Mass Air Flow sensor) connector and ran the car - it was massively better but this time not rev past 3,500 rpm. After re-connecting MAF I drove to the mechanic who plugged in his diagnostic machine and it came up with an air pressure problem and he thought it would be the MAF sensor at fault but cleared the codes and told me to drive it again and see if it re-occurred. Then within 15 miles it went back to not revving past 2,000rpm. I've looked online and I can get a cheap non-oem MAF sensor for cheaper than another go on the mechanics diagnostic.
Any thoughts on what might be the cause? What else I could check or whether it's worth spending £30 on cheap MAF sensor and see if that cures it?

[bcredliner]

Not a good idea to purchase a cheap MAF. Go with OE or OEM. MAF is a critical part of adjusting air/fuel ratio.

I suggest that you purchase MAF cleaner and liberally spray the sensor which are the wires that are not as obvious. Most of the time cleaning the MAF will solve the problem if that is the problem. It is an easy one to eliminate yourself. As far as other causes, there are many possibilities. In the major of cases reading codes and troubleshooting will get you to the core cause faster and less expensive than throwing parts at it. An example of some other possible causes----vacuum leak, fuel pump, gas filter--the list goes on.

[powers1]

Hi Brian.
You got PM.
Stick with Bcredliner sound adivice, and only buy an OE or OEM MAF.
Buy the BOSCH item ref:0928 400 527,but try cleaning yours first!
If you disconnected the MAF and although car was better,the fact it still wouldnt rev past 3500 rpm,means its also another problem not picked up by your mechanic.
No harm in cleaning the MAF as Becreliner suggested.
First you remove the black engine cover behind the air ducts,then remove the MAF (need special torx key to remove the 2 screws), by undoing these scews and pulling it out!You then buy some brake cleaner and spray it on the metal elements and inside the MAF ,then immediately from some 30 cms (IMPORTANT) dry it with compressed air.

Your symptons ,could be EGR ,vacuum pipe leak or turbo itself with the exhaust vanes getting stuck.
Try disconnecting the egr Vac pipe that connects to EGR valve ,first and test!
No change!Then check vacuum system for leaks!First thing you do is remove in and out hoses on vacuum reservoir (this usually cracks) and join them together with a plastic union.Test and if no change,get your mechanic to use vacuum gun on turbo pressure converter IN and OUT hoses and on hose going to wastegate valve.
Let me know how you get on and we go from there.

[treeman]

Originally Posted by bcredliner

Not a good idea to purchase a cheap MAF. Go with OE or OEM. MAF is a critical part of adjusting air/fuel ratio.

I suggest that you purchase MAF cleaner and liberally spray the sensor which are the wires that are not as obvious. Most of the time cleaning the MAF will solve the problem if that is the problem. It is an easy one to eliminate yourself. As far as other causes, there are many possibilities. In the major of cases reading codes and troubleshooting will get you to the core cause faster and less expensive than throwing parts at it. An example of some other possible causes----vacuum leak, fuel pump, gas filter--the list goes on.

Thanks for the advice - I've asked around a few local shops here and they don't sell specific sensor cleaner and the mechanics seem to not have tried this but looking on the internet it appears a common thing to do and it makes perfect sense to me to even do it regularly anyway to make sure it is sensing correctly. I have ordered some CRC MAF sensor cleaner to be delivered so will check it out visually first then spray with cleaner when it arrives.

[powers1]

Originally Posted by treeman

Thanks for the advice - I've asked around a few local shops here and they don't sell specific sensor cleaner and the mechanics seem to not have tried this but looking on the internet it appears a common thing to do and it makes perfect sense to me to even do it regularly anyway to make sure it is sensing correctly. I have ordered some CRC MAF sensor cleaner to be delivered so will check it out visually first then spray with cleaner when it arrives.

This will do
Brake, Clutch & Parts Cleaner - 150ml Aerosol | eBay

[treeman]

Update - I now have some MAF cleaner but I'm struggling to get the MAF sensor off - I have the torx set to get it off but just cant get to the bottom torx bolt to get it off. I'll try again this weekend.

Also I was going to do the EGR check but not sure which part that is and which hose to disconnect - any help welcome...

[treeman]

Update 2 ----

I ran the car yesterday , I did 11 short trips between 2 and 15 miles each and the car ran differently all the time, sometimes not going past 2ooo rpm, then zooming off to 4000 rpm no problem, then slowing down to 2500 rpm. It was erratic with no logical reason.

Also twice from the 11 runs it would not start, just the starter spinning but nothing firing (normally it starts first turn of the key). Both times I found pulling of the vacuum pipe from the right hand side of the vacuum reservoir and releasing pressure it started fine.

This is leading me to think the problem lies with the vacuum pipe or reservoir - any opinions?

[treeman]

Update 2 ----

I ran the car yesterday , I did 11 short trips between 2 and 15 miles each and the car ran differently all the time, sometimes not going past 2ooo rpm, then zooming off to 4000 rpm no problem, then slowing down to 2500 rpm. It was erratic with no logical reason.

Also twice from the 11 runs it would not start, just the starter spinning but nothing firing (normally it starts first turn of the key). Both times I found pulling of the vacuum pipe from the right hand side of the vacuum reservoir and releasing pressure it started fine.

This is leading me to think the problem lies with the vacuum pipe or reservoir - any opinions?

[powers1]

If you cleaned the MAF and its worst ,then you need a new MAF!Does the car run fine with MAF disconnected?
See my post #3 above for how to check vac reservoir and system!
To answer your previous question on what EGR vac pipe to disconnect!Remove the inside black engine cover (the one that goes over the power steering reservoir) and on the right side (looking from the front of the car ) you will an EGR valve connected directly to inlet manifold and you will have small 6mm a vach hose pipe attached to it!Remove and blank the hose pipe with a 6mm M10 screw.Test car with this and see if any different!
With error symptons,like you described ,you most definitely have error codes stored in ECU!
Read it and it will point you in the right direction
You could have a loose or leaking pressure pipe or vaccum!"

[treeman]

I cleaned the MAF thoroughly yesterday and this made no difference. If I disconnect the MAF there is no noticeable difference either. I have looked at the lengths of vacuum pipe and the cotton braided covering is damaged in many places but can't see any defects in the rubber underneath but I have ordered some lengths to replace anyway.
I tried to bypass the vacuum reservoir by connecting both pipe ends together with a piece of 3mm plastic pipe but the car would not start when i tried that so not sure whats happening there - I'm guessing it should at least start unless the seal was very poor maybe?
I'll check the EGR valve when I get some time.
Thanks for the help with this.......