Okay, I have googled and searched forums until I am blue in the face and can’t find an answer to this one. Also sorry for the long post, I just wanted to be thorough in what I have done to it. I bought a 1992 ford F-150 as a fixer upper, it has a 5.0L EFI speed density intake, no MAF. It has 4 speed auto, E4OD, transmission. I had to replace both gas tanks complete with fuel pumps and sending units. Replaced all the brake lines and all brake parts front and back including new emergency brake cables. I then took off the upper intake and removed the fuel rail, I cleaned all of the fuel injectors, put on new O-rings and filters, and pressure flushed them while cycling them. I also replaced the fuel pressure regulator during this and put in new plugs and wires. When I put everything back together it would start and run relatively well. I have not driven it yet, just been redoing a lot on it.

I then started on the interior, rebuilt my Dash and put in a new climate control module, cleaned and repaired the instrument cluster, replaced all the fuses and replaced the ignition key switch. While I was working on the dash, I took the top of the engine apart again. I replaced the EGR valve and the EVP sensor on top of it. I replaced the EGR vacuum solenoid and the EGR pipe to the intake, I put on a new PCV valve, a new MAP sensor, and replaced the EVAP solenoid which had been removed by the previous owner. It does not have an air pump or related parts on it. I also replaced the throttle position sensor, put in a new distributor. I rewired both the positive and negative battery cables with new 4-gauge cable and put on a new power steering pump and new vacuum lines.

When I went to start it after the second round of work it would not start and acted like it was not getting fuel, I traced this down to an error on my part, forgot to plug the fuel shut off valve back in after redoing my door hardware. I plugged it in and now the truck will start right up but will immediately start revving up like it is being given full throttle, I verified the throttle is not stuck and it will do this every time I start it up and does not settle out, it will keep speeding up until I shut off the key. I pulled codes and the only two I have are 327, the EVP is out of range and 121 which was the TPS was out of range, I set the TPS to .96 volts using a voltmeter when I installed it. After this code I checked it on the truck and I am getting 5.02 on the reference voltage, my signal wire was showing 1.66 which is to high and was most likely why I was getting the 121 code. I popped the throttle a couple of times and it settled back to .96 volts. The only thing not testing correctly was the signal return wire which I could not get an Ohm reading on, it would always just show zero when this should be just shy of 2 ohms. I did clear codes and run them again and the 121 code did not come back up but the 327 did.

Does anyone have any idea what would cause the engine to just rev to full throttle every time It is started??

 

You've had the upper intake off twice, go double check that there isn't something trapped in there preventing it from sealing and that the gasket hasn't failed.

 

Thank you, I will check that, I normally use a copper spray gasket sealant on those but did not this time due to reading a lot of people saying they did not need a sealant on them. So that could be it.

 

Sure sounds like a vacuum leak.

I always install the plenum gasket dry. Did you try to reuse the gasket?

 

No, it is a new gasket, but yes I was thinking that somehow it is getting air from somewhere because the throttle blades are not open when it does this, I will pull the plenum tomorrow if it doesn't rain and check the gasket make sure I didn't accidentally damage it when I was installing the plenum.

 

They always used to say, (and still do) that "the third time is a charm"
That said, something entirely different may be happening
Take a fresh look
You need one of these books and to read about 50 pages out of it
I have a Ford Masters cert. That and 5 bucks will buy you a cup of coffee, but
They used to tell us to use the diagnostic subroutines in the PCED that we all thought were junk
Here is one out of my 1993 PCED for idle concerns
The PCED is online at your library on Alldata free to print in most cases

 

 

 

Amazing info, thank you very much.

 

Well... All of that and it had nothing to do with the plenum or sensors at all. As I said this truck was a mess when I got it, one thing that was wrong after I fixed the fuel injectors was the vacuum lines, for instance someone had removed the EVAP solenoid and plugged the cruise control vacuum line into the port on the throttle body During my repairs, I put a new EVAP solenoid back in place and hooked it up where it was supposed to go on the throttle body and plugged the cruise control into a vacuum port. That was my issue, every time the truck started the cruise control would go all out. After I replace all the gaskets again and reinstalled the plenum it was idling the way it was supposed to. Then I realized I had forgotten to snap the throttle cable back on, I did that, started the truck and it went through the roof again. Pulled the vacuum line on the cruise control and it settled down and started idling again. So now I get to verify everything on the cruise control but that will be a future project once I get it to driving.

 

It still does that when you have the cruise/speed control vacuum hose connected to the vacuum tree on the intake manifold?

 

Yes, that is correct, it was pretty late today when I got it all back together so I will go out tomorrow and verify all of the vacuum hoses and wiring on the cruise control tomorrow. Probably won't be doing much troubleshooting of it right now since I have several larger issues to work through first.

 

The speed control system has it's own vacuum reservoir behind the driver side headlamp. It's a small metal tuna can looking reservoir. It rusts out on the bottom. Could be your vacuum leak source.

 

Thank you, I did check that, but it turns out the previous owner had messed up the vacuum tubes on the cruise control vacuum motor itself. The line coming from the reservoir and the line coming through the firewall from the brake were swapped, I flipped them around where they were supposed to go and it will now idle with the cruise control hooked up. Thank you again everyone for your help and input on this. Seems like everything I fix on this truck shows up more stuff that was messed up lol.