weird idle coming off power; coasting

[bryanb]

I found the MAP sensor, and it was tough to get out. I tried to 'clean' it, but couldn't get it apart enough to clean anything significant. No change in the problem.

I can confirm that the problem ONLY happens when decelerating when the engine is warm, and ONLY between 25 and 35 mph in town. and on the hiway, only at 35 on the way down. Seems to me these are shift points or when the torque converter locks or unlocks when decelerating.

 

[Mark_88]

I don't think you can clean them...I would try replacing it outright though...

When my Tempo needed the MAP it would idle way high sometimes when slowing down...and the tach needle would bounce around for a few minutes...and sometimes just die out completely...

Sounds like something definitely is dirty or needs replacing though...did you manage to get any codes? Could also be O2 sensor...or any number of things...try to get codes if you haven't already done so...that would be very helpful...

 

[bryanb]

I haven't tried getting the codes. I haven't seen the check engine light at all, so didn't think it worth the trouble.

I suspect the Idle Air Bypass, but not enough to spend $90 for one. I wonder what the MAP would cost.

This all started after cleaning the IAB, so thats another reason that could be implicated. And I did spray some cleaner in that step motor, so maybe knocked something loose, and now needs replacing?

I'll try getting codes this weekend. I need to do more trouble shooting on the temp gauge anyway. I replaced the sending unit, and im not sure that fixed the non-working gauge either.

 

[bryanb]

both the iAB, and the TPS test withing specs with the volt meter.

Haven't got the computer codes yet, but that might be a good place to go too.

Bigger problem is the water leak into the headliner, and seemingly down the A pillar.

 

[bryanb]

Today, I went for a drive around the block, to warm it up. The problem never occurs when the engine is cold.

to recap, between 25 and 35mph if I let off the gas, the engine will rev for a few seconds. between 1000, and 1200 rpm. if im going faster than 35, it won't happen until I slow down to 35mph, and then it happens. If I just continue to slow down, it'll rev again at 25mph.

After the egine was warmed up, and the problem was evident, I stopped, turned off the engine, and then pulled the connector off the IAB. Started up the truck and drove around the block again.

The problem didn't go away completely, but it was interesting. It seemed to run just fine, curb idle-wise. Not abnormally high or anything. When slowing down, from between 25 and 35, the revving was almost non-existant. When faster than 35, it still revved at 35, but much softer, and slower.

Still can't rule out the IAB, but it is a curious problem.

 

[bryanb]

Hey!

anyone still listening!?!?

I checked the TPS sensor, and the IAC, for impedance, and they are in spec. The TPS voltage changes like its supposed to when the throttle is moved. Though I couldn't get a reading on the IAC from any one of the pins to the housing.

A buddy had a code reader at work today, he was 'renting' from Oreillys. Decided to run the codes for the Ranger, and see if anything showed up.

We did the engine 'cold' since we didn't have much time on break. this is what we got on it.

The KOEO test was all 11's.

The KOER test had a

77 System did not receive "goose" test - see TESTS
thats a minor deal, I assume I didn't goose it hard enough.

13 (R) Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too high)
IAC ?!!?! even though it spec'ed out for impedence? I'd believe that, I guess.

21 Engine Coolant Temperature (ECT) sensor out of range - ECT
Yes, I know the engine was cold-ish. It might have warmed up towards the end of the test. I drove it into work, and then it sat for an hour or so before we tested it.

42 (R) System rich - Fuel control
because engine was cold-ish? or bad O2? it does smell very rich on cold starts, and it getting less than stellar gas mileage.

 

[bryanb]

Ran the KOER test again with the engine hot. Comes up with just the 13.

 

[Mark_88]

When I had my Tempo tested they came up with a list of possible problem areas...the first was the MAP, then the O2 sensor...and I can't recall the third or anything after that...I went with the first one and it fixed it...so you might try working down the list...

 

[bryanb]

New TPS sensor made it far better than it was. Still revs a little bit when letting go of the throttle at around 35 mph only. Also put on a new IAC.

base idle is still way too slow. Around 500 indicated, and like its running on 2 cylinders. I've set the idle: unplug IAC set base idle speed with set screw, and then plug IAC back in, and idled fine for maybe a day, and then I noticed after a trip on the hiway, it was back to its old trick again.

 

[Mark_88]

Wow...monumental issue that lasts 2 years~

How many miles have you put on it since this started?

I did find this about "goose codes"...

http://bronco.zenseeker.net/EECIV.htm

 

[bryanb]

Wow...monumental issue that lasts 2 years~

How many miles have you put on it since this started?

Maybe 5000 miles. I think I'm at almost 229K.

 

[mitchvines]

try the map cuz im having the same issue on my 2002 4.0 and it throws codes for right and left bank lean, with occational misfire. Ive cleaned my MAF, and IAC motor. And everyone that ive work with thats wrenches says map sensor. so ill be trying that. just gotta find it.

 

[bryanb]

try the map cuz im having the same issue on my 2002 4.0 and it throws codes for right and left bank lean, with occational misfire. Ive cleaned my MAF, and IAC motor. And everyone that ive work with thats wrenches says map sensor. so ill be trying that. just gotta find it.

New MAP, no difference. Should I 'reset' the computer first? And to do that, I'd just pull the battery for what 5 minutes?

 

[Mark_88]

It should reset after five minutes...but if not try it for 30 minutes...and yes, it is needed to let the computer reset and if the codes are clear you should be OK...if not...test again with all the new stuff to see what you get...