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I have a 2000 Ford Focus ZX3 Ztech. I've only owned it for a couple of months and only have a couple thousand miles on it since I purchased it with 238k miles on it. When I bought it, it needed a fuel pump and fuel filter because it had been sitting for about 3 years and the fuel in the tank shellaced, but the car ran flawlessly after that and got up to 34 mpg.

It started running rough at idle about 2 weeks ago, but it would start and run. No CELs in dash. I found the PCV hose was deteriorated and collapsed behind the throttle body. I replaced the PCV and line to TB, cleaned MAF sensor, air box, etc.

This did not cure the rough idle--it actually made it worse--hard start without pushing down gas pedal and won't run at all unless you hold it in the 3,000+ rpm range. Let off down to 2,000 rpm and it idles rough and dies. I sprayed the TB with carb cleaner to ensure the butterfly was not sticking, which it does not appear to be sticking.

I then suspected the air idler control valve (based off what I found on the Internet). I attempted to reach the air idler control valve, but I don't have a 12-year old hands and cannot reach it without removing all of the emissions lines to the EGR valve, the EGR Valve and the EGR valve bracket.

I've also read on the internet other possible culprits with the EGR, EVAP canister, EVAP canister vent solenoid, DPFE sensor, vacuum sensing valve, etc.

With the goal of avoiding the dealership, my questions:

1. If I have no CELs and I purchased an OBD II reader, would it give me a code to diagnose if any of the aforementioned parts have failed or need to be replaced? I don't want to take it to the dealer to pay $100 to diagnose if it is something I can do myself.

2. Will an OBD II tell me if the air idler control valve is bad? If so, I will take it to the dealer to repair that since I cannot reach it without disassembling the emissions parts to reach it.

Thanks in advance,
Tracy
 

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Old Phart
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Code reader/scan tool can read codes that are NOT lighting the CEL (pending/inactive types) but it can't read what isn't there yet. Not all faults are possible to detect by that system, including the IAC not working properly as long as it's still OK electrically.

Fuel pressure CAN be checked by a scan tool, and since you didn't mention whether the whole pump assy. was replaced that could easily be your problem.

As far as reaching the IAC, it's necessary to do so from underneath and do it by feel.


There are many other possible issues at that mileage, including jumped timing from an old belt. Compression test would give a good idea of basic condition, and could point to a timing issue without deeper investigation to prove it's correct. At that mileage it's due for it's 3rd or 4th belt/tensioner/pulley kit, depending when prev. replaced.
 
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