Mudman604

i have a friends 1988 f150 5.0 5 speed 4x4. he had a super low idle, and did not run to well i offerd to help him fix it. at this time we have replaced TPS, MAP, IAC, plugs, wires, rotor, distrib cap, and now the computer.

ive got one or two more ideas but im not shure. first we replaced the tps plugs, cap a rotor, it ran pretty good for a week or so, then is got worse. when releasing the throttle, it would start surging to find idle then would stall most often. ater that, we did the plug wires, map and iac. did not help much, stalling was a little bit less frequent. them i took out the computer and opened it up, found two leaking capacitors, so i ordered a new ecm, installed it, took a day of driving for the ecm to adjust decently, (owners name is josh) he says now is cruising real good, had good power, but it runs super fat and still surges most of time, but hasn't stalled, so it is drive-able atm.

have checked a few times for a vac leak with non-chlorinated brake clean, soaking all the vac lines, and the intake manifold ext. did not affect the engines speed. after the new ecm and w couple days of josh driving it, i read the codes, got 33, 41, 63.

33 is EGR but from what i understand that should not be causing the problems im having,

41 Haynes manual says No Heated O2 sensor switch detected. right side (i though there was only one)

63, TPS low. which is weird because ive probed it and set the TPS to 1 volt with the throttle set screw, and it still gives me 63 after i cleared the codes by removing the jumper while key on. and also the engines idle IS affected if i disconnect the TPS while running, so the computer is getting something from it.
i dont know

putting this out there if anyone has any ideas please shoot them, i will look into the o2 now, that was one of my ideas, the next was stuck injectors.

Steve83

Stop replacing parts unless they fail a published test. Test any replacement part the same way, to make sure it passes. I'd reinstall all the original parts and start diagnosing from scratch.

Spraying toxic flammables onto a running engine is dangerous & expensive. Use a mechanic's stethoscope or 3' of garden hose to pinpoint vacuum & exhaust leaks.

Don't pick a word or part name out of a code definition - when you post a code number, include the COMPLETE definition. The list in this caption is specific to these trucks:


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You should NEVER tamper with the throttle stop screw, for any reason. It is NOT for adjusting idle speed or air mixture. Use the procedure in this caption to reset it:


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If the EEC is setting a fault code for a condition that doesn't exist, the EEC is defective. But you MUST measure as close to the EEC as possible so you're measuring what it's measuring. Use pierce-probes (as linked in this caption) or backprobes.


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Injectors do not stick open. They only stick closed after an engine has been abandoned for ~6 years, but it doesn't hurt them.

Mudman604

thanks for the reply, but i want to try to understand a few things now, my understanding seems to be insufficient. first, why thease parts were replaced.

the orange wire on the tps was cut when i got to work on the truck, i repaired the wire, the tps still did not give an output, so we replaced it.

plugs and wires were old and needed replacement. rotor and cap were worn.

as i explained the next possible causes, josh just said to (go ahead and replace them) that being the map and iac, i was hesitant because i did not want to throw parts at it like that, but he insisted.

after all of those parts replaced, like i said i inspected the computer to find the leaking capacitors, which i understood to be a common thing.

the throttle stop screw had been tampered with before. as it has signs of using pliers and does not take much force to turn not like it was still glued. i tryd adjusting it attempting to correct the TPS voltage too low code. i did not see a problem with this because my understanding was the computer basically had full control of idle with the iac, me adjusting the screw did not affect the idle as i expected obviously because the computer compensated for it. my understanding though is clearly mislead.

all of old parts, map, iac were thrown out. (inexperience i guess)
and ecm had to be traded in for core.

for code 33 is a continuous code, EGR valve not opening, my understanding this shouldn't cause it to run rich like it does. but im not sure now.
41 continuous, No HEOS switch detected
And again 63 i believe if i remember it was a continuous code, wich is probably why it did not get erased? if i remember i got 11 (system pass) then 111, separator code, then these codes. i apologize for not stating that, i forgot about it.

the brake clean was a suggestion from an experienced employee at the local auto parts store, we used the Non-chlorinated brake clean, so not flamable vrs me being told to test with starting fluid or propane, booth i decided against.

also, reading through the steps for setting the idle, i dont remember there being any holes or orifices in the butterfly valves, so then what?

also sorry for the mashed up top post, its been a while for me posting on forums, bit rusty
P.S. awesome bronco steve

Steve83

The EEC doesn't have "full control of idle"; it has limited control, and it relies on everything being in-spec & as-built to work right. But that's not the only reason it's so bad to tamper with the screw. The throttle plates can become jammed in the bores, causing damage or loss of driver control.You're still posting shortened versions of the code definitions, which is probably part of why you're confused. Read the definitions at the link I posted. If the EEC doesn't detect it, either it didn't happen, or the detector (sensor) isn't working/installed properly, or the system that activates it isn't working. Any of those can throw off several other operations & measurements, which could potentially result in a rich condition.Again: wrong definition for your truck. Read my list, which comes from the '92-96 Ford PCEDs.That's not what "continuous" code means - it means it's stored in continuous MEMORY because the fault is detectable even when NOT in self-test modes.No EEC can produce both 2- & 3-digit codes. You either remembered them wrong, or you read them wrong. Either way: it makes ALL your code numbers questionable, which makes all your definitions & diagnoses moot.Chlorination has nothing to do with flammability. Chlorinated brake cleaner produces phosgene gas when heated, but all brake cleaners are flammable.Ignore that & follow the procedure for resetting the screw.

Mudman604

the truck is 88, for all codes in my reply, i read the definitions from that list for two digit codes used till 91. and my mistake for the 111, i have the notes from when i recorded the codes, 11, 11, 33, 41, 63, 33, 41, 63
i do understand what the code for egr meant, but since it could be causing the rich condition, i will diagnose what is not allowing the egr to function next.
41 c No HEGO switching detected
copied from list, will need to check o2 sensor then correct?

and will reset screw.

where would the VECI decal be located so i know what timing base to be?

Steve83

You're right - I stopped at 41r. But no: the HEGO isn't a likely cause for the HEGO not switching. It's more likely that the engine is actually running constantly rich (or lean). Messing with the HEGO or replacing it won't fix the fuel mixture.

Your truck info should be in your signature so it appears automatically with each post. Click this & read the caption:


(phone app link)

The VECI on an '88 will probably be on the air filter cover, but it might be on the core support or hood. It should be easy to find, though. But the base timing for all EFIs is 10°.


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A common & easy-to-check cause for a rich condition is a ruptured FPR diaphragm.


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Only CHECK it - don't buy or change it unless you actually find it leaking.

Mudman604

alright. sounds good, will check FPR, and then set idle screw properly. thanks again
like i said in the first post this is a friends truck, i personally dont own a truck yet.

Mudman604

@Steve83
Checked it today, FPR is busted, disconnected vacuum line, engine immediately picked up a little in rpms, but idled smooth, took about 20 seconds for fuel to spurt out of fpr, but it is whats broken. Thanks for the help again.