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Idling rough

I have an 01 Focus with almost 130k on it. For the past three weeks or so it has been idling very rough and occasionally stalling. Once underway it runs perfectly normal and gas mileage hasn’t changed. The CEI is on, but I haven’t had the opportunity to get the code read yet. The funny thing is that with the a/c on the car runs much better. It will still sometimes stall, but it runs much smoother until it does.

Post back when you get the scan results.

I will, it may be a bit before I get the chance to get it checked out. I was hoping someone would have an idea based on the fact that it runs better with the a/c on. There are no autozones etc around anymore to get it scanned for free. I haven’t posted here for awhile; I love the fact that you don’t have to wait anymore to post a question.

The most likely suspect is a dirty or faulty idle air controller, but error(s) will help narrow it down.

If it does happen to be the idle controller, is that something I can clean or replace myself? Also, if I had to pay to fix it roughly how much could I be looking at?

I’m taking the car for an oil change in the morning and the mechanic said he’d also get the code for me. If it is the aic, what should this cost? I may have him fix it on the spot if I know the price is reasonable.

it may be a bit before I get the chance to get it checked out.

 That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here. 

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.

Thanks for the info NYBo and Joseph. I’ll post the code later this morning after I receive it.

My wild guess is the Throttle Position Sensor (tps). On my Mustang the tps failed intermittently over nearly a year. The car would sometimes stall at idle and with the A/C on the engine would rev up and down until the engine stalled. When the A/C turns on the engine is supposed to speed up to adjust for the increased load of running the compressor. Maybe the tps is no longer accurately measuring the closed throttle position so the engine stalls at idle. When the A/C is turned on, the tps is told to rev the engine and it successfully does that at least enough to prevent stalls.

Here is a photo of the 2001 Focus 2.0L throttle position sensor: You can probably see it on top of the engine and replace it yourself. I also suspect the tps because numerous manufacturers (Airtex, SMP, ACDelco, etc.) make replacements and lots of Focus throttle postion sensors are sold. But it is still just a guess from a remote location!

Here is the idle air control (iac) valve:,APP426514/vehicleId,1130202/initialAction,partProductDetail/store,1140/partType,00207/shopping/partProductDetail.htm Disconnect the white plastic electrical connector, start the engine, and see what happens. If it idles smoother, it could be the iac valve, or the carboned up passages to its pintle and from it. Carb/Throttle Body cleaner, and round wire brushes will remove the carbon…

These are the codes: 402, EGR (excessive flow) and 171 (too lean). The mechanic said 402 is likely causing 171. Does this sound correct?

Yes, a stuck open EGR valve could cause the engine to run lean. Ask your mechanic to use Carb/Throttle Body cleaner, and brushes, to clean the passages in the EGRs internal passages. The carbon could be keeping the EGR held open.
The EGR valve could be getting the command from the engine computer to stay open, too. In that case, he’ll have to find out why.