my 1988 302 (5L) engine,auto tranny has the following problem:
when I am coasting, after just letting up on the gas pedal, the idle will be at a steady rpm for 5 seconds, then it will drop to a lower rpm and be steady at that rpm until I touch the pedal again. It's almost like a jake brake affect. Is this an engine problem or a transmission problem?

 

sounds like the beginning of my problem i had . check the engines section on my post .

 

try cleaning the throttle body and the valve next to it. is it bolted with two bolts and has a plug in sensor. it's on the right of the throttle body. clean it with carb and choke cleaner. i would try this first.

 

your refering to the idle air control valve .like i said b4 look for my post where pkrwud helped me get my truck running right . it is all more or less explained there.

 

I think I have the same problem '91 f-150 302 4x4 5spd (250,000 km). Truck shudders, just did complete tune-up but I think TPS switch may be going-a couple of times,when cold engine rpm increased while shifting gears- I read your posts in engine section but its a little incomplete-what did it turn out to be?

As a side note of just finding this website, I finally got rid of that annoying ping thats haunted this truck since about 100 000 KM. By re-routing #8 plug wire, I have spent hundreds on trying to get it fixed, no one knew-not even the dealer(many years ago though)

Thanx in advance guys!

 

Ahhh yes, the famous Ford crossfire. You would be amazed by how people ask my advice, and don't listen when I suggest seperating their wires. Oh well, good for you! As I recall, Ray's problem was the MAP sensor, but that doesn't mean that's what your problem is. Your description sounds like a problem with the Idle Air Control valve (IAC), which is mounted to your TB with two 10mm bolts. These should be disassembled and cleaned with CRC Brakleen (red can) every so often. What have you done so far? Have you performed a KOEO and KOER self test yet? If so, what codes did you get? If not, I would recommend going to your local auto parts store and buying a Ford Code Scanner. For about $25, you get a tool that makes pulling codes a breeze, as well as an instruction book to guide you and answer several questions. once you get the codes, it becomes much easier to fix your problems.

Take care,
-Chris

 

Chris
No I haven't got A ford code scanner yet-Just recently lost all faith in my mechanic-backfiring thru intake with shuddering-he said rebuild time-burnt valve-took it to a pro he said pistons normally burn from fords pinging not valves-advise problem is external...although a con rod bearing clatter is starting. Just waiting for a friend to send mitchell on demand to check TPS voltages. When my wife gets home with the truck I'll check the IAC.
I'll let you know how I make out.
Thanx

 

Buckshot .
i was backfiring through the intake also . it was the MAP sensor . i too feared the worse . but i did a compression test . it was ok . vacuum is good . all the parts i had problems with that i had replaced and it still ran that way til i replaced the Map.

 

Just got back from the Walmart with the code reader and Chiltern manual-now lemme see... did I mention I'm an hvac mechanic not truck-found the map senser and tps-let me try to figure this code reader out

 

Still trying to figure code reader out (got sidetracked because of truuck shudderind broke MTA tube into exhaust,got that leak fixed now)

Tryed unplugging IAC motor at idle-engine DID NOT stall-RPM went to 500 from about 700-ohm tested it and was within specs-I see a new gasket where it attaches and I think my mechanic said no more cleanig-next time replace. Maybe its time-What do you think???

 

Hi Guys
Reset codes and drove

More info-it looks like KOEO codes are 11-11-12-93-13-22-93-13pause and then 2? Am I reading this rightt--whats 93-coast clutch solenoid circuit failure?

Do these codes have to be repaired before KOER

Also created vaccuum leak at vaccuum tree and engine idle sped up-does that mean its a fuel problem?

Any help or insight is greatly appreciated

 

buckshot . the hard codes are reading normal it seems to you explaination . was there a pause after the two times of code 11 then one beep or flash then the other codes came up ? there is two classes of codes stored in the ecm for koeo . first is hard codes or codes present NOW. then a 4 second pause one flash or beep then another 4 second pause . then it starts the KAM codes or keep alive memory . these codes have been problems in the past but are not present at the time you tested it . read the manual that came with the code scanner it will explain this more .
and yes all koeo codes need to be fixed before you can do the koer test . start with the first code given and work you way up the list . sometimes when you fix one problem others will go away also . good luck and let us know what you find

 

12 is a hard code . it was probably 22 and not 11 . then kam codes were 93 , 13 and 22 again .first set of codes will read twice in a row . second will read all codes then read them again a second time . code 12 and 13 both relate to the throttle position sensor . you need to test the voltage coming out of it at both idle postion and wide open throttle postion . it is the green and black wires i believe . 22 points to the map sensor . you have no means to test this . but you also may have misread the code . check it again after reading this and the manual for the code reader . 93 is the coast clutch solenoid circut failure . (e4od, your tranmission ) hopefully this was read wrong also . chris can shed more light on this then i can . again good luck

 

Yes there was a pause and rewriting it could it be: 29-31-32 and then the codes repeat: 29-31-32.

29-yes,my vehicle speed senser and speedometer don't work
31-PFE, EVP or EVR
32-EVP voltage below closed limit

What does this mean?

 

31 and 32 both point to the evp . or the egr postition sensor . this could be a result of a sticking egr valve . check the vacuum lines from the egr valve for breaks in it or melting . mine was plugged up and i replaced it with a piece of rubber vacuum hose .
that hose runs to the evr also refered to a egr valve relay . all this info the computer gets from the evp . so it could just be a vacuum line or a sticky egr valve.