Newbie here so please keep that in mind.

I have a 1990 Ford F150 with the 302 5.0 and I've recently just started troubleshooting low engine idle on cold startup. Temperature here yesterday was 39F and idle stays around 700 RPMs. From what I read on cold start, it should hit somewhere above a 1000 RPMs and stay for a while until the engine starts to warm up and gradually come back down until it goes into Closed Loop, then relying on the O2 Sensor [Have one ready to go in, just haven't been able to get the one currently installed out yet].

I started with the ECT and replace it. The old ECTs connector is spinning freely from the brass housing so I'm assuming it's bad / disconnected on the inside? I tested it with my DVM and couldn't get a reading on the 200k scale. If I remember correctly it was reading .052 on the 2M Ohm scale. When I replaced the ECT, I didn't have the battery disconnected. In hindsight, I think I should have. Anyways, after the ECT change, startup was the same, 700 RPMs or so. However this time, once the temperature reached 150-160, something changed, idle dropped to around 650 if I recall and then it started bouncing around, eventually stalling out. Could this be the PCM going into closed-loop with a faulty O2 sensor?

As far as my limited education goes here, the O2 sensor isn't involved on initial startup but rather the ECT, so why still the low idle speed? Another sensor involved in initial startup? I'm willing to learn here folks and test what is needed, answer your questions, etc. I've ordered http://www.ebay.com/itm/191802608089?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT by recommendation in another forum regarding EEC-IV Fuel Injection Operation hoping that there is some information in there that might connect the dots. This truck has been in my family for 26 years so I'm doing my damnedest to keep it alive.

 

Let the truck reach operating temperature, then shut it off and check for codes.

It'll be way lighter on the pocket book and easier to diagnose and troubleshoot.

When you retrieve codes, post them here.
Also, you will get either 11 or 111 for system pass. If you post that you checked and didn't get any, further work is needed.

Let us know what you find out! And Welcome to FTE!

 

Thanks for the fast reply. Will do. I have a code reader, just didn't have time last night to run through them. I will try today on lunch and report back. I appreciate any and all help from you guys.

 

No luck. For some reason or another, I could not get the test routine to start running on my Innova 3145 reader and then ran out of lunch time. I did, however, before hand swap out the ACT sensor. The one that was removed was covered in black oily soot but resistance checked out as I breathed on it and blew on it.. Still after the ACT change, low idle on initial startup. I checked the voltage on the ACT sensor socket and it read 4.5V. I know these are suppose to be around 5V so could half a volt be causing me grief?

Since I did the engine warm up routine I went ahead and tried to loosen the O2 sensor but it's not giving.. I've already ruined two O2 sensor sockets so I think it's pretty much rust-welded there. I don't know that it has ever been changed..

Problems, problems..

 

Ok, so now, can't get the code reader to communicate. You can try a nail file and clean the contacts.

Does the Check Engine Light come on when you turn the key to the Start/Run position? It should stay illuminated until turning the key while trying to crank and start.

And the ACT/ECT sensor should see no higher than 4.60vlts. That's maximum for sensor output. It may vary between 4.50 and 4.70 with KOEO.

Let us know what you find.

 

I'm pretty certain the CEL wasn't on the entire time when I was trying to do KOEO. I'll double check this evening. Any thought right off if the CEL comes on and then goes out before starting what that indicates, other than a problem?

I think my voltages are on then on the ACT/ECT connectors if that is the case on the voltages. I'll let you know what I find out from the KOEO when I can get the reader to initialize.

 

Take the idle air control valve off, an try cleaning it. Verify the plunger inside moves freely.

I generally use box-end wrenches to take O2 sensors off. Often times the plug will slip through the box end of the wrench.

Not going into test-mode could mean the connections are dirty, or there may be some problems with the computer.

 

Thanks Lead Head, I've heated the engine to normal operating temperature [190F thermostat, verified on a mechanical gauge in the cab] and worked on the O2 sensor two separate times now. I honestly don't think it has ever been changed. When at normal operating temperature, I've used the box-end with a cheater-bar to no success.. I've also ruined two O2 sockets in the process as well.. Heated up to near-glowing red with a Benzomatic torch and still a no go. I really don't want to have to go through the process of cutting that section of pipe out and redoing the bung weld but that may be the solution.. I did see where AEM makes a No-Weld accessory but I'm wondering how the gasket that seals everything would hold up over time. Here's a link to the AEM product. No-Weld O2 Sensor Mounts | AEM

Anyways, while I'm 90% certain the O2 sensor needs to be replaced, I'm not certain it's contributing to the low idle issue on cold start. Last engine run up, the sensor wasn't even connected. As far as the IAC, it was replaced a couple months back when diagnosing warm idle issues. That turned out to the barometric pressure sensor, passenger side firewall.

 

If the CEL doesn't illuminate when first turning the key to the Start/Run position, the code reader doesn't Communicate with PCM, then I'm betting the PCM is at fault.

With the age of the vehicle, your symptoms with idle problems, code reader not communicating with PCM, then its highly possible and probable that the PCM is the culprit.

If the capacitors are the problem, you may be able to save it.

 

I agree 100%. Time to pull the PCM then inspect for signs of leaking capacitors.

 

Even better just replace them. 26 years in a harsh environment is well past their intended service life and just looking at them isn't a useful test.

 

There is merit in that suggestion. I'll second that!

 

Well the cost is low compared to the damage that can be achieved I'm thinkin'. $5 worth of capacitors and a soldering iron and they will be good to go for another 20 years. As an aside I have my doubts if some of the really modern vehicle will be maintainable going forward, at least on a practical level.

 

OK, sorry for the delay folks.. Work, kids, home life, etc etc.. I finally beat the O2 sensor loose and replaced it. Many many coatings of PB Blaster and Liquid Wrench later.

KOEO
11 - O
10 - Separation Code
33 - C

I think the 33C is possibly prior to me changing the EVP sensor on top of the EGR valve sometime back. I really probably need to clear Continuous Memory and drive around and see if the code comes back. I'm going to be replacing valve gaskets soon so when I have the plenum off to get to the passenger side valve cover, I'm likely going to replace the EGR hose and valve then.

KOER
8 CYL
10 - R
12 - R
16 - R
77 - R
52 - R
12 - R
16 - R
77 - R
52 - R

Something else weird has transpired over the last few days, I believe since I changed the Engine Coolant Temperature Sensor. This happened yesterday but truck was at normal operating temperature and idling fine then started running rough and died. Thinking "that's strange" I tried restarting and the engine would turn over, start and immediately die. What the crap! Tried this a few times and same result.. I let it sit for 20 minutes or so and tried again, same result. Switched to the rear tank, started right up with a slight hesitation and all was well.

 

Your codes are pretty normal if you forgot to turn the wheel or goose the throttle during the KOER test. The only out of the ordinary one is the idle control code.

Have you checked your fuel pressure?