Increased idle speed

[ptjs1]

In an attempt to eradicate a superfluous periodic error code that indicates a MAF range error, I cleaned the throttle body on my 2004 4.2 N/A car. It wasn't a full clean as I didn't dismantle the body from the car, but I gave the throttle disc, spindle and mating surface a good clean with carb cleaner.

Now every time I start the car from anything other than hot, it immediately fires at about 1700 rpm and takes about 45 - 60 seconds to pull the revs down to normal idle speed of about 625rpm.

I haven't dismantled it again yet to check if I have disrupted the disc return spring home position but can only guess that the cleaning has caused this in some way. It seems surprising as I assumed that a cleaned disc and mating surface would mean that the throttle was more able to fully close, whereas I now have the symptoms of a slightly opened throttle.

Has anyone got any experience of very fast idle from cold on a 4.2 with a new or thoroughly cleaned throttle body?

Tks

Paul

[J44EAG]

I had a similar glitch, Paul, on my 4 litre.S-type.

I found I hadn`t quite put the ducting trunk and rubber collar back correctly.

Worth also ensuring that breather pipes from the rocker cover are internally clean and sealing well on the O-rings. Maybe also check all other pipes to ensure they are sound and fitting well to their relevant parts.

The throttle plate in the throttle body will snap to the close position rapidly if all is good. Oily residue and crud needs to be completely clear around the closing edges when at the idle position.

I can also say I`ve had a MAF sensor issue in the past. Whilst not showing fault codes, replacement with another unit transformed the running of the engine. Worth spray cleaning the hot wire in the MAF as that can get coked up and produce odd readings to the ecu.

Hope this might give a few ideas..

Mike