Hi all

Got a few issues with my 197k 2005 4.4

The idle is very low, maybe around 500rpm which makes the whole car shake. Occasionally stalls when coming to a stop when cold, and very occasionally get 'reduced engine performance', also only within the first minute of driving, never when warm.

The fault codes I have are:
P0171 - Bank 1 too lean
P0174 - Bank 2 too lean
P0175 - Bank 2 too rich
P0316 - Misfire first 1000 revs
P0302,302,303,304,305,306,307,300.

Runs beautifully when driving, maybe feels a bit down on power under 3000rpm but no signs of a misfire at all. I've also never had the check engine light illuminate.

Any ideas where to start? Going to try and investigate it in the new year, would like some opinions before I start throwing money at it!

Cheers!

 

Need to clean the throttle body.

Crud building up just inside the valve causes reduced airflow at low revs, which in turn causes the engine to stall when decelerating and coming to a stop at lights etc.

The reduced O2 in the exhaust will be sensed by the Lambda sensors resulting the car trying to compensate for it and going rich. At higher speeds the build up of crud has less effect and the engine runs normally.

Clean the throttle and all should be well.

 

In addition to cleaning the throttle body, clean the air mass flow sensor. Both cleaners are sold at any auto part store and even Walmart.

 

Cheers for the input, I'll get the throttle body and MAF cleaned and see how I get on!

 

careful with the MAF cleaner, they have a tendency to be super fragile. Cleaned mine with no problem but I have seen a LOT of warning posts on other forums.

 

I'd start with cleaning the throttle first and seeing if it runs OK, then decide if the MAF really needs to be touched. There are just times when you should leave well alone.

 

Ignition coils would be my guess.

 

In general this would present as a specific cylinder misfire, in which case you'd swap a known-good cyl. coil with the problem cylinder. Clear codes, restart, and wait for CEL then check codes. If the code moved to the new cylinder, then you know it's a coil (without spending $.01) In this case it doesn't seem to be a specific cylinder misfire.

In this situation (idle, or low-revs) I'd look at something like a dirty MAF or for our LRs, the ever-dirty throttle body butterfly.

The next step diagnostically would be a vacuum leak, for those who don't believe me - try pulling your dipstick when you're at idle. I have a perfectly-running LR3 and it just about falls on its' face when I do this. This is indicative of, and similar to, a vacuum leak of some kind, somewhere.

Next would be sensors of some kind - although your options are limited due to the fact that you said the engine runs well in mid-higher RPMs.

Personally my bet's on a nasty throttle butterfly and a small vacuum leak somewhere (as a diagnostic-focused restoration mechanic and owner of many LRs).

 

Well I actually experienced bad ignition coils and it presented on multiple cylinders. The issue is that they don't like the heat so if the engine has ever overheated it can kill a few all at once. Or if they are all ran beer the same conditions multiple can fail or become weak around the same time.

 

EstorilM it's funny that you mention pulling the dipstick, I've noticed slight signs of oil coming out of the dipstick despite it feeling quite tight