I posted this in another thread, but decided it's wasn't nice to hijack the other person's thread, so here is my own:

I have the same problem on my 90. I haven't bought a code scanner yet, I was hoping to avoid that for awhile for financial reasons. Basically the trucks acts up pretty consistently when it's cold or damp out, and only occasionally when it's fair outside. When it running good, it's wonderfull. When it's not, it's terrible and embarrasing. On a bad day, you can start it and it will fire right up, then after about ten seconds just die. After several restarts, it will finally stay running but surge terribly between 400 and 1200 rpm. I can even feel it surging while I'm driving, meaning I can feel it suddenly lose power, then a few seconds later restore. Once I've driven it awhile, it will warm up and get better, but even then if I sit at a long stoplight it will idle nice for a few minutes then suddenly revert to the surging.

It has a very recent tune-up with quality parts, no junk Autozone crap. I recently did all the upper engine gaskets (except the heads) because I had a bad intake gasket. When I did the upper upper engine gaskets, I throughly cleaned the throtle body, IAC and intake runners with carb clean. This was last fall and the truck ran like a Lincoln until this started about 2 weeks ago. I haven't changed anything else, I don't want to just throw parts at it. I suspect a few things could cause this though. I suspect the fuel pressure regulator, fuel filter, IAC and maybe something in the ignition. I guess I could even see a bad fuel pump causing some of these problems.

I would love to hear some ideas about which way to go.

-Jimmy

P.S. I already endure a lot of heat for not having a grocery-getting SUV like every other Yuppie in my office, but it's only worse when they hear my truck chocking and stalling in the parking lot. Please help!

 

I would check out some of your emission control lines and acessorys. I had a similar problem with mine and it turned out to be a clogged carbon canister along with a couple of cracked vaccume lines.

 

have you replaced the fuel filter? DW

 

OK, I will check those things, but you HAVE to tell me where you found the cool gauge overlays for your '90! I have looked everywhere, and can only find gauges like that for the newer '92 and up Broncos. I even called a place and asked why the '92 and up Broncos have a different gauge overlay since they look the same to me, but I never got a good answer.

As for the emmisions stuff, I never knew the canister could become plugged? I've never replaced or serviced one. If it has become plugged, doesn't that indicate a poor dirty running engine much like when a catalytic converter gets plugged?

-Jimmy

 

TPS

 

I got the guages from procarparts.com they are listed for the F 150 (same thing)

 

What Harry said...mine did a lot of the same things, took about 2 years before someone suggested the TPS and sure enough, it fixed THAT problem.

 

Have you tried the fuel pressure regulator ? Mine did the same thing a few years ago and that's what it was. Two wana be mechanics couldn't find it but Haynes sure did.

Good luck,

 

I do suspect the fuel pressure regulator, but I haven't replaced it. I hate throwing parts at something just to try. Yesterday I filled up the tank and added two bottles of injector cleaner, and today it seemed much better by the time I got to work. I wonder if I just had a tank of bad gas, or maybe some dirty injectors, or both? I think I'm giong to borrow my buddies fuel pressure gauge and take a look at the fuel pressure while it's idling cold, assuming the problem hasn't gone away already with the fresh gas.

 

That's funny, when you look up the Bronco hauges on that website, they only list one type of gauge kit, and only for Broncos without a tach. If you look at the same year F150, they have 3 kinds, and only for F150's with a tach!

I have one question, when looking at the two kits I'm interested in, one of them looks just like yours. In the center of the tach and speedo there is a large lumminescent circle that seems really bright on the pictures. Does that annoy you at night? The other gauge kit doesn't have those large circles, but the numbers and markings look the same. I'm just trying to decide which one I like best, and I thought those big bright circles might annoy at night.

-Jimmy

 

It comes with a dimmer switch... so there is no problem there.

 

Well this weekend I replaced the fuel pressure regulator, and TPS sensor. I also cleaned the throttle body and air bypass valve because they were both pretty carboned up. After starting the truck and realizing I wasted a prefectly good fuel regulator and TPS, I tried a few other things. I unplugged the coolant temp sensor, which cause the truck to REALLY run bad and stall. So I'm pretty sure the coolant temp sensor is working. I also unplugged the vacuum line to the EGR and that didn't make a difference. My plugs, cap and wires are almost new (about 6m months old) and they are quality Autolite parts. I am at a total loss. I've made an appointment to take it into the Ford dealer tomorrow (GASP) which will be the first time I've paid someone to work on one of my vehicles since I was in high school. When they finally track down the gremlin, I'll post back in case anyone else ever has these same symptoms.

-Jimmy

 

If it's only when it's damp out, it's probably something electical. My first guess would be cheap plug wires. My dad's 78 elcamino did that after a tune up with crappy big A parts (thank goodness thier out of buisness now) One day when it was really rainy, about a month after the tuneup and problem started, opened the hood and it looked like the 4th of july the wires were arcing so bad. Replaced with premium napa belden, no more problem.

Ofcorse, the newer bronco has more electronic devices that could be affected the same way, like the tps.

 

Yes, I've experienced cheap plug wires also. I had a set of Autozone wires on my minivan and every time it rained I couldn't start the van.

I learned my lesson with cheap parts a long time ago. These are premium Autolite 8.5mm hi-energy wires with pure silcone jackets. I sersiously doubt they are responsible. But then again, I can't find the problem so I guess I better not rule out anything.

 

Well I promised I'd post back when the dealer found the problem. Unfortunately it's bad news!

Turns out (and don't ask me how this is happening) the engine has severe blowby and low compression on ONE BANK ONLY. So the computer is reading lean on one bank and rich on the other. It can't possibly adjust the idle in these conditions, and hence the lopping surging idle.

The possible reasons the dealership gave me:
1) worn rings on one side (this is the dealership's primary guess)
2) bad valves or valve seals on one side (dealerships secondary guess)
3) blown head gasket on one side (my guess)

Doesn't really matter which of the above is really wrong, since they all tell me I'll soon be pulling the motor and tearing it apart for a complete rebuild. Might as well do it all at once right? Just goes to show you how little "mileage" really counts on a vehicle. My 88 Voyager with 220k miles still runs like a top, and my 90 Bronco with 95k miles has a worn out engine!

-Jimmy