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Erratic Idle When Warm And Runs Rich

2898 Views 11 Replies 5 Participants Last post by  GreyHawk
Installed at the dealership a new mass air flow sensor and sensor assembly, and brand new thermostat because the car was stalling and idling rough. THis didn't fix the problem, The dealer then said ECM, so a rebuild ECM was installed. Still have the problem. Idles fine when cold but goes into a rough idle when warm. Notice that there is black smoke from the tailpipe. Where to look check next?
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I had similar problems with our Taurus... it also ran well when cold but when it got warm it ran rich with black smoke. It also didn't want to start when engine was warm. These problems started straight after I overhauled the transmission (AXOD). It was strange because before the overhaul the engine worked just fine :huh:
I thought it must have something to do with the thing that I had removed the engine for transmission overhaul. So I checked all the electrical connectors of the engine and found out that the Coolant Temperature Sensor connector was loose. I pushed it in and that's it: it started to run normally, hot and cold :banana:
It seems to me that Your car has similar symptoms so I would first check that sensor and its connector. Seems like Your engine doesn't get the temperature information correctly...
Where is that thing located? The coolant temp sensor?
What I have found and have done so far. The problem got worse, lost power and would barely run at idle, and wouldn't run when giving it gas. Removed a hose from the pipe going to the EGR and got it to rev up giving it gas. Replaced the EVR sensor. Still didn't run above an idle. Checked the compression well within limits. Checked the vacuum, and found at Idle it was about 5 and 0 when giving it gas. Disconnected the cat from the front it got vacuum to about where it should be and giving it gas the engine speed increased and the vacuum gage acted amost normal. Ordered a cat and will be putting in on when it arrives. Also going to replace the Temp sensor and Ox sensor. Will post after al this is done.
I agree with 88STW, I read that if the Temp sensor is not functioning properly (or if disconnected) that it will signal the PCM and inturn this will cause the engine to kind of go into a fail-safe mode as not to damage it by overheating it, then it starts to operate like you disribed, I think it very common on a lot of late model Fords. :eek:
saerandy: The coolant temperature sensor is located on top of the engine, beside the distributor (well, at least in our model of 3,0L V6). It's pointed upwards in a rather tight place, so it's not so easy to notice if it's a little loose. Those connectors are made of a plastic that gets really brittle in cold and the safety clip cracks easily. I "safety wired" the connector in place to avoid disconnecting it by mistake again...
Got the new cat on along with the water temp sensor and O2 sensor. Car starts and runs great even revs up. A little back smoke when it is first started which goes away. However, the check engine light came on after about 10 min and went back off. I pulled codes (which may have been saved) of 184, 337 and 647. Cleared the codes and will post if anything else happens. I only have a few sensors left to go..... then they will have all been replaced. Also put new headlight housings on.... no more frosty and damp headlights :banana:

184 - MAF sensor - signal voltage is higher than expected.

337 - EGR valve postion (EVP) sensor, pressure feedback EGR(PFE) sensor or EGR pressure tansducer (EPT) signal voltage to high.

647 - Transmission problem - incorrect gear ratio obtained for third gear.

Thanks, 88STW!!

I have been looking for that thing for a while. I think it needs replacing.
After clearing the codes and driving the car for about 50 miles, the check engine light came back on and the following codes are 172, 173, 184, 647

172 - HEGO - voltage signal indicates lean bank#1

173 - HEGO - voltage signal indicates rich bank #1

184 - MAF - signal voltage is higher than expected

647 - transmission problem - incorrect gear ratio obtained for third gear.

Still surges at idle... lower acceleration. This seems to be related to the MAF which is new. If the MAF is messing up I can see how the HEGO is going lean to rich. How do I check the output voltage of the MAF?
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those are all problems related to the MAF sensor. The MAF also determines shift points. I would take it back to the dealer and make sure they got the right MAF; also check to make sure it's plugged in fully.
to check the MAF voltage, backprobe the signal and ground leads (pins 2 and 4, IIRC), and start the car. the idle voltage should be between 0.5 and 0.7v. Increase RPM, and the MAF signal should increase to about 1.5 to 3.0v.
It appears that the MAF that the dealer had installed was bad. Installed another MAF and all appears to be fixed. If there is a problem I'll repost in a new thread. Thanks to silvapain and information he supplied. :chili:
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