Situation: A shop recently performed an intake induction service on my car. After picking up my car and driving a few miles, the engine began revving to 5000 rpm by itself in neutral (I have manual trans). I took it back to the shop the next morning and was told (mechanic just turned on the engine, but without any further inspection) that it is probably to due to the chemicals used to clean the system and it will go away after some miles on the highway. That evening, I put on 100 miles, but the problem persisted - the car will speed to 70 mph on the highway flat without pressure on the gas pedal.
After bringing the car back to the shop, I was told that the IAC unit was bad and needed to be replaced. I was also asked if anyone had worked on it before because it contained silicone - No one worked on the engine except for them.
Thereafter, I took it to a Ford dealer and the problem was diagnosed as a bad IAC valve and fixed for close to $600. At least the car works afterward. When asked, the dealer said that an improper induction service could damage the IAC, though they can’t say for sure.
I don’t believe the local shop intentionally damaged the car (shop has a good local reputation from the online sources and BBB that I checked), but I told them it was “hard to believe” that this problem was coincidental. They denied any blame.
Question: What is the probability that the IAC unit gets damaged by an improper induction service routine?
A) Background:
I have a 2004 Ford Focus with a 2.3L PZEV engine and 100k miles. I am the original owner and the car has never had any issue. The only engine related maintenance is periodic oil change.
As part of an oil change/annual inspection in NY, I recently took it to a local shop (one that I did not use before) to check out a weird clanking sound emanating from the engine compartment (sounded like a hole in the exhaust to me). The sound was particularly loud as I accelerate. I also mentioned that it idles a bit rough and seemed to hesitate on acceleration. However, engine does not cut at idle and runs fine.
B) List of things the shop recommended:
Must do:
Broken cross links which must be replaced to pass inspection
Suggested things to make the engine run better:
Change air filter
Change brake rotors and pads
Change the spark plugs
Intake Induction Service
I had everything suggested performed except for the rotors/pads (pads still good) and air filter (I said the 2.3L does not have a normal air filter - weird that the shop suggested this).