Throttle body question???
 

Hi Everyone, Problem with my 2001 E53 4.4. On a Cold start, engine Idle rpm will hover around 800, at warm to full running temperature, engine rpm stays at a consistent 1100-1200. (Transmission in park or neutral, of course when in gear it'll drop to 700-800 rpm). Yes, there are two codes: P0174 and P0171. Indications of Banks 1 and 2 running too lean. Perhaps a vacuum leak? If it was a vacuum leak, wouldn't it have a high engine rpm no matter the engine temperature? What common denominator would give a lean condition to both banks? My thoughts have "leaned" towards the throttle body. Took a peak at the throttle body, found that the throttle plate is not completely closed (key off/eng off). Shouldn't the plate be closed completely? Hoping someone can enlighten me on this plate. P.S. The engine runs great, very strong running, even with the lean condition. Thanks to todays engine mgmt. No doubt, Stoich

The throttle plate will not be closed tightly, it's unlikely that the throttle plate stop adjustment is your problem unless someone has tampered with it. Way more likely that there is a vacuum leak.

if you have a scanner that can show fuel trims then use it to figure out if you have a vacuum leak. You can also use that along with brake cleaner (spray to suspected areas) to detect leaks if you don't have a smoke machine.

running lean is not good since the ecu is dumping more fuel to compensate, the condition is not at its worst condition yet because eventually it will misfire.



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Virtually every car I've ever worked on gets those codes. Almost always it's an intake vacuum leak somewhere. In my case it was the intake boot the offshoot hose or the back at three cracks you could put your finger into


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The brake cleaner or start pilot will probably not help if you can't monitor fuel trim or lambda very precisely (graph). I tried and got nothing but with the smoke test found leaks.

I'm not sure there are any leaks that won't be common to both banks considering the central intake. The good point is you probably have only one leak to look for.

Some things to check:
- Intake boot
- PCV hoses (including the one beneath it that goes back to the oil return)

Good luck, solving one leak already massively improved my fuel economy...