Greetings all, I have a 2001 VDP and have chased down more problems than you would care to hear. But, recently I was getting the codes 171 and 174 (both banks lean) and the knock sensor code (308?? for the bank 2) I changed the Knock sensor with a new Britpart item and immediately the knock code was gone but the car will not idle. It runs fine after 1200 rpms but under stumbles roughly and then stalls. I suspected the air mass sensor since I was getting the lean codes, so I unplugged it and voila! it idled, a bit rough but it never stalled out. So I bought a new mass air sensor (Walker brand) and now have the same issue, runs fine over 1200 but wont idle. Unplugged the car will not start.
So, would you expect I have a duff new sensor or am I barking up the wrong tree?

 

Cracks in the air intake tube bellows area? Don’t toss the Denso MAF sensor!! Clean out the old sensor with brake cleaner and blow it out with compressed air.

 

No cracks in the intake tubes, I checked that by spraying starter fluid around. I also have tried cleaning the old MAF sensor with CRC MAF sensor cleaner. No luck there.

 

Get a Denso MAFS.

 

I have purchased the new $250
Denso sensor, installed, and now have exactly the same symptoms as with the old Denso sensor. Still will not idle but runs quite well at above 2200 rpm’s.

Does anyone have any less expensive ideas as this sensor cannot be returned.

 

Other areas to check:
Part load breather corrugated hose on drivers side valve cover to throttle body elbow.
Full load breather on passenger side air intake tube.
Intake manifold gaskets.
On both sides of the intake manifold (under the covers) is an air pipe that joins on the backside of the throttle body. O rings.
Brake booster vacuum pipe specifically under the throttle body on the passenger side. There’s a very specific size o ring under the black plastic “quick release” clip inside the brass insert. C2S15816 Use only the clip and o ring from that.

 

Thanks, I found a slight vacuum leak at the throttle body where the plastic booster line fits in. Another leak at the junction of the air pipes you speak of. That is a very expensive piece, I may try to repair it if I can release those stupid Norma clips without breaking them. C2S15816 is on the way.

 

I have received and installed the c2s15816 coupler and still have the same idle issue.
I now suspect some issue with the part load breather. I see one end on the cam cover, the other on the purge valve but where does the middle fitting go? I don’t think there is a vacuum leak there but there has to be one somewhere. I placed a plug in it but that didn’t fix the idle.

 

My advise on all posts like this is smoke machine. I have a thread on how to build one.

 

What is the status of your secondary tensioners? Sounds, to me, like the timing is not correct: a jumped chain. . .

 

Ewww..... that could get nasty....and expensive.

 

Tensioners are good, no worries there. I began to suspect the part load breather since it had been "customized " by a previous owner. They had broken the Norma clip holding the breather to the throttle body and with the booster line leaking also I did not see that. New breather line on the way, and I am confident that is the problem. Thanks all.....