Ok, here's the problem(s): I bought the truck from an older gentleman who had rebuilt the top end of the engine and went blind before finishing. The truck starts and runs just fine except for VERY high idle....got to be in the 2500-3000 rpm range. I have the vacuum diagram, but I need to know what diameter hoses to use, and if that would even account for such high idle. There were bolts missing from the intake manifold that I replaced already, but I have tried the brake cleaner spray diagnostic and can't find any additional leaks. Any ideas?

 

I think you're on the right track. if it's not bad gaskets around that two-piece manifold then check all the lines. might also be some bad senors somewhere. did you check to see it the computer was putting up codes?

 

Thanks for the response. Its actually out of inspection/registration, so I am hesitant to drive it somewhere to get the codes read. I guess there's really not much else I can do at this point until I run the codes though...maybe its something really obvious that will turn up on a scanner.

 

a scanner costs less than $30. amazon.com sells them for ~$22. but there is a way to check the codes without a scanner. I don't have the link though but maybe if you do a search you can find it. for as cheap as a code reader is I just go that route and it makes it simpler.

 

Ford Fuel Injection » How To Run a Self-Test

Sounds more like you still have a vacuum leak. Pull the connector to the Idle Air Control solenoid (IAC). If the idle remains high then that indicates there is most likely a vacuum leak or someone has turned up the Idle Stop screw on the throttle body.

If it drops down to normal then you have a sensor issue or bad PCM.

 

thank you rla2005. with that link you can check the codes without a reader. keep us posted.

 

Again, thanks to all for your help. I ran out and got the code reader (thanks for the heads-up on that) and got the following codes.


332 Insufficient EGR flow detected
452 Vehicle Speed sensor fault
116 Engine coolant temperature higher or lower than expected
411 Cannot control RPM during KOER low RPM check
412 Cannot control RPM during KOER high RPM check
538 Insufficient RPM change furing KOER dynamic response test
632 Overdrive transmission Cancel switch/no action during self engine run test

Several of these are probably not related (other fun problems to deal with down the road) but maybe one of you can decipher this into something that points with more certainty to what my problem is.

I will go out and pull the connector on the idle air control to see how that turns out.

 

Update: just pulled connector on the IAC solenoid and there was no change.

Wouldn't it have to be a fairly massive air leak for me to be in the 2500-3000 RPM range? I almost believe I can hear a pulsed hissing from the engine in sequence with the RPM's, but the engine noise is too loud to tell for sure when its revving this high.

 

Also, what is the function of the "coffee can" on the passenger side wheel well of the engine compartment? It has a vacuum line going in, but none coming out. I have the vac diagram, but there is no reference to this and I have never dealt with it before.

 

the code 116 might mean a bad temp sensor which might cause the truck to increase rpm to warm the engine faster. that coupled with a vaccum leak may possibly be part of it.

411, 412, and 538 are probably because of whatever is causing the truck to idle so high.

I'm assuming you don't have a tach since it seems you're kinda guessing on the RPM at idle so it's possible it's not as high as you think.

 

just pulled out my haynes manual(don't know what I did with my chilton's) and looking at the troubleshooting guide one of the thigs to check is a leaking EGR valve. your truck is throwing an EGR code so check there.

my manual has a lot of info just on the EGR system and checking it out in relation to idle issues that wouls take way to long to cover here so you might want to pick up one. I've seen repair manuals like chilton's and haynes at my public library so if you don't feel like dropping the cash on one you might want to check there.

 

Most vacuum diagrams refer to that "coffee can" as the VRES aka Vacuum Reservoir. It is well known to corrode and rust through over time.It stores vacuum for use under low vacuum conditions, i.e. acceleration, going up long hills, etc. It can cause EGR valve operation issues, TAB/TAD solenoid errors and high idle because it is a HUGE vacuum leak.

 

Codes 116 is usually caused by not warming up the engine and transmission before running the KOEO tests. Codes 411/412, 538 and 638 are typically user error induced during the KOER tests.

Code 332 can be caused by a leaking Vacuum Reservoir, no vacuum to open the EGR. Code 452 indicated an issue with the speed sensor input in the last 80 cycles. Not relevant at this point in time, but you may want to pull the VSS in the rear axle, clean it off, then re-install at a later time.

 

So here where I'm at today...I have a hose that goes into the Vacuum reservoir (coffee can) but no hose coming out of the other fitting on it and no idea where it should go to. So thats an immediate vac leak diagnosed. (the vac reservoir does not show up on my very unhelpful vac diagram) It also appears that even some of the vac hoses that are currently hooked up aren't where they should be. Does anyone have a photo/link to where I might actually be able to lay eyes on a real world engine to see where the vac lines should go? Been to every auto parts store in Austin and not a single person has a clue so far.
Also, I think its best at this point to replace all the vacuum lines with new ones, since some of the old ones are a hodge-podge of electrical tape, barb fitting splices, etc. Is there specific diameters for each line, or can I use one universal diameter of hose for each line?

 

Once again, I can't thank you who have posted advice enough. I replaced some hoses, and still no change. However, I went to the EGR solenoid and pulled the line out to the EGR valve to check for vacuum, and found no suction whatsoever. So I pulled the vacuum source line that did have suction and plugged it directly to the EGR valve and there was an immediate drop in the RPM's. Would this indicate that the EGR solenoid is bad, or is there some other explanation?