Hey guys got bad new problem on the truck but here’s a little background. 89 f150 I6 EFI 4x4. Intitial issues was a fueling problem and after much head scratching and throwing parts at it it was the in tank fuel pumps which the PO said were replaced. Then I had a high idle issue, vacuum leak which took forever to find between those endeavors I changed the following: iac, fuel pressure regulator, all 3 fuel pumps, fuel tank selector valve and switch. The vacuum leak turned out to be the lower intake plenum had the bolt hole closet to the fire wall snapped of. Took it to a local welder, reflex gasket and replaced my vacuum lines and boom no more vacuum leak.

my current issue is low idle. On start up it start high fire a few seconds which is the initial warm up then it drops to about 500 where it should be at 750 while it’s still cold it had trouble staying running. It will bounce from about 450-550 and sometimes dies. If I drive it around and It warms up the idle is still low about 500-550 but is more steady. I tested to tps and it was right at .95. In spec from what I’ve read and on the higher end too. I’m wondering if it’s something with the iac which was replaced but when I unplug it there is no change. Not even a check engine light. The computer is working, when I unplug the tps I get a light. Any ideas?

 

I had a truck do this. The solution was the IAC.

To test the IAC, remove the iac all together.

Apply 9vdc to the two leads and see if the motor moves the valves in the iac. Youll want to apply the voltage rapidly in a on and off cycle. If this passes, check for voltage at the harness itself.

It could easily be that the idle set screw was messed with as some time as well. Let us know what you find

 

Ill test the iac when I get off this weekend. It’s brand new I replaced it early on a few months ago when I started this whole ordeal. Thank you for the testing information. I already tested the harness and I was getting about 12-13 volts. When he engine almost dies I’ll get voltage drops but that’s to be expected. I know the battery is new and the pretty sure the alternator is good. I tested it multiple times with the high idle because my volt meter in the dash didn’t work for awhile. I also order all new ignition parts I’m thinking the spark plugs may be bad also Im not sure the state of the rest of the ignition parts so it’s due anyway. I’ll definitely keep you guys posted. I haven’t pulled the spark plugs yet so I don’t know their condition yet.

 

It is good to just check everything. Start woth timing, spark plug wores, plugs, cap rotor, so on. Let us know what you find.

 

So I replaced the ignition components, plugs wires cap and rotor and ignition coil.. timing was good(yes I removed the spout and used the correct mark) Had a hard time trying to test the iac with what I had on hand so I went to oriely and did a warranty exchange. Put the new one on and at first it worked. Cold start 1500 rpm then dropped to about 9 then stayed around 650-750 rpm. Took a quick spin came back and now it’s struggling to stay alive again. It has more of a hunting idle now still about 500 but it will jump to 750 every now and again. After the ignition parts i did a test before the iac defiantly sounds smoother. But still have the issues. I don’t know where to go from here.

 

So I’m currently at a loss. When I pulled the spark plugs the rear most ones were fairly wet so I’m worried that the piston rings my be shot. I’m going to pick up a compression tester and test it Monday. Not sure if that’s the issue like I said earlier when I swapped the iac today it acted perfectly. Started cold 1500 rpm after a minute it dropped to about 800 the 650-750. Took it for a quick spin got back and has the same issue again. 500 rpm struggling to stay alive but will jump to about 750 but then back to stay about 500. So if anyone has any ideas please let me know.

 

With the prevalence of leaking capacitors in the PCM on these trucks I highly suggest you pull the computer then open it up for a visual check.

 

when I initially got the truck I was fighting a high idle and did just this. The computer is fine.
it’s not the maf either I replaced that early on as well. It’s not the air filter low idle with the air filter hoses removed.

 

If you have not run diagnostic codes yet, I think it may help somewhat isolate the issue.

 

Hey all here’s an update. Unfortunately during the weekend I didn’t get much done. Had to leave town for the holiday. When I came but just for s**** and giggles I replace the temp sensor and the Iat because I read this could cause an idle issue. Not sure if that was the issue but the iat was pretty crusty so I’m glad I replaced it. It didn’t seem to do much but ran a little smoother Hardley noticeable. But again after a quick drive low idle again. I ran the codes and all I got was code 67 which I read on another thread was due to me not having the clutch in. In stored memory I had low tps voltage but that’s probably due to me when I unplugged it to see if it would make any difference, same with low egr voltage. I was recording the flashes with my phone and It stopped recording when I started the engine. Don’t know what those codes were and I unplugged the battery to clear everything and I plan to retest later with a fresh memory so I know whatever is stored isn’t the issue. On a hunch I had the original map sensor lying around so I swapped that back in and it seems to work. When it drops to 500 rpm I give it just a tiny amount of gas and then it settles around 700 and stay there like it should. Then if I rev it up or go for a drive it will settle around 500 then I give tiny amount of gas 700. I’m thinking maybe the throttle body is sticking. I’m not sure. I’ll try cleaning it but again I’m back at work. Yay. Any ideas?

 

If you have the 4.9 and standard shift, you must have the clutch depressed the entire time you're running codes, otherwise you are getting nothing. Engine should be at operating temperature and you should run key on engine off codes first. Any codes that appear must be fixed before you go to key on engine running test.

 

Incorrect. You don't have to keep the clutch depressed to get codes.

 

The innova handbook says you are incorrect.

Page 29 paragraph 4 of the

INNOVA 3145 Ford Digital OBD1 Code Reader" target="_blank">INNOVA 3145 Ford Digital OBD1 Code Reader

INNOVA 3145 Ford Digital OBD1 Code Reader">INNOVA 3145 Ford Digital OBD1 Code Reader" /> INNOVA 3145 Ford Digital OBD1 Code Reader">INNOVA 3145 Ford Digital OBD1 Code Reader

code reader handbook states "For 4.9L engines with standard transmission: Press and hold the clutch until all codes are sent (steps 4-10)

You may OR may not have to depress the clutch to get codes if you are jumping the EEC. I don't know because I use the code reader and because of the clutch needing to be depressed is also the reason they sell the extension cable so you can sit in the cab while you DEPRESS the clutch and see codes. SANDY

 

Sandy, you always have the best information.

I use the Innova reader on a 95 with the 4.9. I have NEVER held the clutch in and I have ALWAYS been able to read codes. The only difference is you get a code for the clutch being engaged.

If you HAD to hold the clutch in, WHY would there be a code for CLUTCH NOT DEPRESSED? What use would that code be? You'd never see it IF YOU HAD TO HOLD THE CLUTCH IN TO GET CODES.

You are ONCE AGAIN incorrect on ANOTHER computer-related topic. But I guess your high post count means you know what you're talking about?

 

"Press and hold the clutch until all codes are sent." See the word ALL? I guess I should believe you and not the folks that built the reader and wrote the user book. And I really don't give a flip about what your truck does or doesn't do.

https://static.summitracing.com/glob...s/equ-3145.pdf