My spouse'* '03 GMC Envoy has a problem that is proving to be quite elusive. On 9/24 took to Dealership because car was trying to stall whenever a/c was engaged at idle. They replaced the throttle body which seemed to resolve the issue; however, my wife complained to me that it didn't feel right and within a few days couldn't get the car to go over 50 mph. I test drove it and everything appeared to be fine, except when I pulled back into the driveway it was leaking coolant. Back to the Dealership, replaced water pump and investigated problem. No codes being thrown, they're only solution was that maybe the brake calipers are sticking and causing friction (brought about by them having replaced the Power brake booster on 9/16). There is no evidence that this is the case. Meanwhile, the mpg has gone from averaging around 18 to averaging around 7. Dealership has now had the car in their possession for a week and have yet to determine the cause. My frustration cup overflows! Can anyone help me, please? Oh yeah, almost forgot to add that the cooling fan now appears to be in need of replacement.

Gm had released an update to the engine control module programming for engine stalling due to low idle. I believe it also affected the cooling fan operation. How are you calculating your mileage. Never go by your dic information alone. Calculate at every fuel up and then compare. Did the reduced engine power message come on at anytime?

I don't trust dealers to begin with. But the common issue with the stalling at idle is carbon build up on the butterfly. You just clean it and put a new gasket on and it'* good. Sounds like they messed something up while they were messing with it.

First of all, thank you for the responses. To Chevy82, I calculated mpg the old fashioned way, and when did that ECM update you referenced come out? Don't believe that a reduced power message ever came up.

It'* been out for a while. I'd ask them if they checked for calibration updates for the PCM. Referring to Jws comment, not all dealers are bad. Just because a couple of bad experiences left a bad opinion. I work for a very reputable and friendly dealer who will do anything to keep a customer happy to some extent. I take great pride on what I do. Truthfully some independent shops and shade trees here, I wouldn't let touch my car.

Just got back from dealership, they say they've been in contact with GM for tech support, but all they get is "drive it until it throws a code". They claim that the car has been hooked up to the machine and that all applicable updates have been completed.

I have had dozens of times that when it comes down to it they don't know what they are talking about, but you ask anyone of them, they know there stuff. I can only think of one out of dozens that I would let touch my car. He raced at the same track as me and his car was one of the fastest small blocks there. That is not a real good ratio when you consider my other dealings have been technical issues with newer cars which used to be the whole reason you would take it to them.

I'm sorry you've had bad experiences in the past. Dealerships and techs with that type of attitude give us good dealers and techs a bad name. I won't work for huge dealers, all they seem to think is money. I currently work at a small town dealer about 7 techs. Real good company and dealer.

To the O.P. With that much fuel mileage drop something is wrong. When was the last tuneup? Alignment issue ( Too much inner toe or recent damage)? Fuel gage operating correctly? Seen some times fuel gage sender not reading right giving that impression.

Honestly sounds like they like to shotgun parts instead of actually fixing it.
What'* wrong with the fan?

Game over. Went in yesterday to check on progress. They hadn't done diddly squat! Options given were: 1- leave it with them and they will drive it when they can see if an idiot light comes on, or 2 - take your car, drive it, track your mpg, and bring it back in IF an idiot light comes. In their own words "We just don't know what else to do". The cooling fan has recently been kicking on intermitantly for no apparent reason (but the car actually threw a code on that!) and they want $1000 to replace it! I am no longer the owner of said vehicle as I refused to throw any more money at it. Used it as a trade-in and cut my losses. BTW, I will NEVER take another vehicle to that shop for any reason! Thanks for your input guys.

Even if you're on the right track, you'll get run over if you just sit there.
Will Rogers