Hopping for a little insight on diagnosing a problem I am having on a truck that I bought. It is a 1999 F250 v10 6.8, auto, XLT. I bought the truck with a bad transmission, so I have never driven it. I bought it from a guy living at 6,500ft elevation I live at 8,500ft elevation if that could make a difference. He said the truck ran great before the trans went out a year ago, when buying it I fired it up and it sat there and idled without an issue reved up without an issue. I got it home started right up pulled it into its parking spot with no issues.

The surging idle problem started when I pulled all the fuses and relays one by one to make sure that was not an issue with the trans. I have since gone through the fuse twice including scotch brighted off all the fuse ends. I would think that since that is when it started it could be coming from fuses or relays, but nothing points back to it.

I now have a good trans in the truck and still have the issue along with a P0103 code. It is very hard to start, if I get it started by holding the pedal to the floor I can get it stay running while I keep giving it gas to 1500 rpm. Then after about 20-30 secs it just shuts off.

Diagnosis I have done so far: verified, signals at the MAF, verified that MAF output changes through voltage and scanner, pulled the MAF everything looks clean and fine, no vacuum leak on PCV, brake booster. I have drained all the gas put in 90 octane gas, new fuel filter. Previous owner said he had replaced the MAF at some point.

The truck has Cold air intake, throttle body spacer, and no muffler after cat. The ECM is possibly not stock, but I pulled it and there is nothing to indicate that it is not stock.

Suggestions on where to go next.

 

Check fuel pressure .

 

Checked fuel pressure while trying to start its at 38psi after about 2 hours of sitting its at 20psi.

I was able to get it to run longer than 30 secs by keeping it at 1500 rpm and when it went to die I blipped the gas a couple of times to keep it running. I got the coolant up to 125 before it died. I was not able to restart after that until it sat a while. I can get it to start after about 10 -30 of trying and it dying. Once it stays running for a bit there is really no restarting it.

If it was the MAF or IAC it would, but just not very well correct?

 

Unplug your battery for a while to clear the codes and then start over.
Begin by chasing the codes. P0103 is Mass Air related. Dig deeper.

 

Thanks,

Unpluged battery a couple of times, just tried it again for about 15min with headlights and ignition forward to drain any residual. I rest codes a couple of tries ago of trying to keep it running and there were no codes before I disconnected the battery. Started it this time same thing and no code came up. I took a video last night of scanner and this is the readings of MAF to RPM
LB/M
MAF = RPM
41.74 = 1575
42.96 = 1725
44.78 = 2114

 

Mine did that a long time ago...IAC Idle Air Control Valve was an easy fix.

 

Sounds about right