Idle Air Control or Throttle Position Sensor - TCCoA Forums
 
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post #1 of 5 (permalink) Old 06-02-2018, 01:21 PM Thread Starter
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Idle Air Control or Throttle Position Sensor

My Cougar has issues with take off. It bogs down and has little power till the engine gets to a higher RPM then takes off. The car also idles lower than suggested in the specs. From the research I did, it could be IAC or TPS (or both?) that can cause this. I put my code reader on the car and had no codes (of course), so I am having to component level testing. I have replaced the IAC with a used one a few years ago after cleaning it out. The car ran fine and up till the last 6 months ran fine. I did take the car on a long drive at high speed and the Check Engine Light came on for a few seconds and went off and the car has run better since than. The issue also seems to be random. Some days if takes right off and others it like the engine needs some Geritol.

If I just replace both IAC and TPS, I am looking at about $80 for both.

Since I could not get any codes to come up, anyone have any suggestions on how to else to diagnose this issue?

Thanks!

PS: The low idle could be due to a mis-aligned throttle intake adj. screw. That I can adjust with my code reader and a screwdriver.

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post #2 of 5 (permalink) Old 06-02-2018, 03:50 PM
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Don't adjust the screw.

If it idles, ihe IAC is probably ok; you can swap it, it's over 20 years old now.

Get a Motorcraft part unless you like diagnosing and replacing it every few years.

Clean the throttle body, and the egr passages. Don't break the egr tube, they're rare.

Pull one of the spark plugs, while the engine is cold, and measure the gap.

If it's over 0.060, replace the plugs with new ones, as well as the wires.

If you pull the plugs with the engine hot, there may not be threads to put them back into.

How old are the o2 sensors?

Also, what engine do you have?

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post #3 of 5 (permalink) Old 06-02-2018, 04:27 PM Thread Starter
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Hi Grog,
I have the 3.8l.

Plugs and wires are relatively new, replaced them all less than 2 years ago and do not put much mileage on the car yearly. Also replaced the injectors when I did the top end rebuild.

Both the IAC and TPS from RockAuto are Motorcraft that I picked out yesterday.

The throttle body and EGR where cleaned less than 2 years ago when I did the top end rebuild. But since most of the driving in this car is shop hopin' for grociers, the EGR could be the issue.

I have been avoiding it, but should probably do a compression check to see where I stand on rings. Valves are fairly new since I had the heads redone recently.

I will pull a few spark plugs and see what they look like (cold of course).

As for the O2 sensors... Not since 2007. Replaced them with new ones from NAPA.

So, with all the work done and more than listed, I suspected the IAC and TPS since the symptoms are very similar.

I did cross my mind that maybe the EEC going bad...

Thanks!

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1994 Mercoury Cougar XR7 - 150k and still going.

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post #4 of 5 (permalink) Old 06-03-2018, 01:26 PM
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It's DTC-less problems like this where live graphing OBDII monitors come in very handy. I've used mine more for DTC-less troubleshooting than code ones.
You can watch realtime response from the TPS to check for dead spots in the control. Of course, another easy way to do this is to put a meter (analog if you don't have an analog bar graph on your DMM) on the TPS pins and check for smooth/clean operation.

I've managed to "restore" my IAC and EGR several times via cleaning.

Of course, if the IAC has failed electrically, replacement is the only solution. I suggest a thorough cleaning then test for plunger operation via 12VDC bench supply (or the car battery) — do not apply power continuously, just quickly tap one end of a test lead to the supply or battery terminal; if it's not dead, you should see (and perhaps hear) it moving.
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post #5 of 5 (permalink) Old 06-03-2018, 07:05 PM Thread Starter
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Quote:
Originally Posted by Torque View Post
It's DTC-less problems like this where live graphing OBDII monitors come in very handy. I've used mine more for DTC-less troubleshooting than code ones.
You can watch realtime response from the TPS to check for dead spots in the control. Of course, another easy way to do this is to put a meter (analog if you don't have an analog bar graph on your DMM) on the TPS pins and check for smooth/clean operation.

I've managed to "restore" my IAC and EGR several times via cleaning.

Of course, if the IAC has failed electrically, replacement is the only solution. I suggest a thorough cleaning then test for plunger operation via 12VDC bench supply (or the car battery) — do not apply power continuously, just quickly tap one end of a test lead to the supply or battery terminal; if it's not dead, you should see (and perhaps hear) it moving.
Hi Torque,
Thank you for the suggestions. I pulled the IAC and it was clean inside, but that does not mean much other than the fuel / air flow is probably good and not running rich. At this point, with the age of this IAC and the problem has stopped, I am going to buy a new one. The prices is very reasonable for an IAC compared to years ago. And just based on age of this one (junk yard replacement when the last one crapped out) and from the research I did, they can have intermittent problems before complete failure. Since most of the possible problem parts on the car have been replaced, it makes more sense to replace it.

I have yet to pull a spark plug, but will take a look later this week (honey dues this weekend). The car actually runs pretty good now but it could act up again if the IAC is going bad.

Again, thanks for all the input.

PS, Will give the TPS test a try as well with a DVM.

1995 Lincoln Town Car Signature Series - 200k!
1994 Mercoury Cougar XR7 - 150k and still going.

I've had too many other cars to mention...
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