1988 Ford F150 - 302 V8 Fuel Injection-AC-PS-Auto Trans

Yesterday morning (10/16/14), all was well... Drove truck 6 miles to do property work. Truck sat for about 4 hours. Finished work, attempted to start truck:

Truck started normally BUT instead of either starting at a fast idle for a short time then dropping to a normal idle... OR if the engine was still warm, starting at a normal idle, the starting rpm was at an unusually low idle. So low that shifting into gear caused the engine to stop running.

In restarting the engine a few times, I noticed that the "Check Engine" light was on (first time ever). Eventually I managed to get the engine to stay running but the idle rpm was/is still lower than normal.

Today (10/17/14), Both fuel tanks being low, I poured 5 gal into one tank just to eliminate a low fuel problem. Engine starts quickly BUT:

1 -Cold engine starts at a very low rpm... not the normal Fast Start.
2 - Check Engine light is ON.
3 - Hesitation exists when slightly engaging gas pedal BUT engine does not die.
4 - The "Check Engine" light goes out when I increase the rpms.
5 - A quick pressing of gas pedal... engine acts for a fraction of a second like it's out of time (bucks), then catches and races normal.

Going out this morning again... will fill fuel tanks. I'll see if any other irregularity exists and report back.

 

Which engine? I assume it's fuel injection, not carburetor?

First thought is a bad IAC (idle air controller). The CEL is probably on due to low oil pressure at such a low RPM. However, it wouldn't hurt to check the EEC for trouble codes.

http://www.examiner.com/article/how-...ensive-equipme

 

1988 Ford F150 - 302 V8 Fuel Injection-AC-PS-Auto Trans

GLC... Sorry I overlooked entering that info. I replaced the IAC awhile back but don't remember why. I'll check my records, then double check my work.

I also went into the hyperlink you provided, copied/pasted and will print it out for reference, thank you.

Used the truck today, filled the fuel tanks, no change in the low idle... stalled many times. The truck has gauges, no idiot lights... charging great, oil pressure at 5/8 of gauge even at low idle.

 

Then the CEL should be storing codes.

 

Installed new IAC Saturday 10/18/19 and just made matters worse. No improvement and the idle dropped lower yet to a point whereas the engine would not stay running unless throttle was applied.

Removed new IAC and reinstalled my original IAC... Idle is still too low but engine will at least run. I'm going to check the ohm reading of the unit and the voltage input first today, then try to read and understand the code readout.

Any thought as to why the new unit would result in a worse problem... new but faulty?

 

Latest Update: MY age may be against me as I've been having a problem understanding how to read the codes... 2 seconds here, 4 seconds there, I get confused. However I will be trying it again and eventually get the knack of it. I have the "Haynes" 1980 thru 1996 manual that covers this specific truck and have been studing it closely... why does Ford make it so complex?

What I have accomplished to date is as follows:
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Ohm reading of IAC solenoid should be between 7 to 13 ohms....

Original and new IAC solenoid read exactly 9 ohms. Presently using original IAC unit (within limits).
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Voltage read at IAC solenoid should be approximately 10/5v....

With harness connector attached to IAC solenoid and turning key ON, voltage jumps to 9.75v "BUT" stays there only 2.5 seconds, then drops to zero.

With harness NOT attached to IAC solenoid and turning key ON, voltage jumps to 10.5v "BUT" stays there only 2.5 seconds, the drops to zero.
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The above according to the "Haynes" book tells me that I am not receiving the proper signal form the ignition modeule?.... Is this correct?

The ignition system on my truck is the TFI-IV setup and apparently has nothing that we would normally refer to as a powerpack, pulsepack, ignition module attached to a fender apron... BUT... rather has a small distributor ICM module mounted in the side of the distributor. This would be the brains of the setup, replacing a powerpack, pulsepack, remote ignition modiule,... is that correct?

As it stands, am I looking at a failed unit within the distributor?

 

Codes as received were: 63, 63, 1, 51, 61, 63, 33, 51, 61, 63, 33

I found that the ECT (engine coolant temperature) sensor was damaged, actually in two pieces... replaced ECT sensor. There was no improvement.

 

You may need a new TPS, read this:

http://easyautodiagnostics.com/ford/...sensor-tests-1

Looks like you also may have an EGR problem (code 33).

Pull the vacuum line off the EGR valve and put your finger over the line. If you feel vacuum and the idle increases, there's something wrong with the EGR control system. There should be NO vacuum at idle. If there's no vacuum and the idle speed doesn't increase, the valve itself could be partially stuck open, remove it and clean it or replace it. If you put a vacuum line on the valve and suck on it, the idle should decrease and possibly even stall.

 

Checked the TPS via instructions... Tests prove TPS to be faulty. New TPS will be ordered and installed soon. Will report back after installation.

The EGR valve vacuum test shows no vacuum. I haven't tried the test vacuum line to see if the idle decreases yet. I'll read up in the Haynes manual to see how to remove and clean it.

 

I'm back GLC. I've had so many things to do since November of 2014 that my truck go put on the back burner so to speak. But finally, yesterday and today, I got back to it.

The EGR valve seems to check out okay so I'm leaving that alone for the time being.

The TPS checked out as being faulty and replacing it returned the starting idle to where it should be... a fast idle at first, then a gradual drop to a normal idle within a short period of time. Many thanks for your helpful advice in this matter.

Question... There is a carbon build up on the throttle body butterflies, and also there is a small amount of heavy caking carbon just inside the top intake manifold opening. The engine hasn't idled perfectly smooth for quite some time... close but not perfect, a little roughness to it. Valve stuck open, burnt valve? Easy fix not likely?

 

Pull the throttle body and clean it, stick a rag down the intake and clean the carbon off around the opening too. Throw some Techron in the gas. A compression test should tell you if you have a stuck or burnt valve, reading the spark plugs should tell you if any cylinders aren't up to snuff. Cap, rotor, plugs and wires all fairly new and a quality brand?

 

Thank you for the speedy reply glc, I do appreciate it. Although I still do most of my own vehicle work, getting at those spark plugs at my age (83 in Aug) have become quite a chore to get at and I may leave that compression test and latest s/plug reading to a local shop.

The dist cap, rotor, and plug wires are way overdue to be replaced I'm embarrassed to say. I will replace all of that shortly.

 

That in itself could be causing it - replace cap. rotor, wires, and plugs.