Have been reading the threads about idle problems and stalling at lights etc. Everybody points to the IAC but thats clean. Some said it was the throttle positioning sensor. I haven't yet checked with a multi-meter, but disconnected it while motor was idling poorly and the idle went up a bit and sat perfectly. Does this mean the TPS is faulty or is it supposed to do that ? Any idea's.

 

Pull the codes please.

http://www.troublecodes.net/Ford/

 

Now wait a minute......

You disconnected the TPS with the engine running, and it kept running? And in fact it idled up?

First of all, this should have set a latched code, as well as put the vehicle in limp mode. Secondly, it would have had NO way of modifying the injector output other than the MAP, which is primarily for timing, but does also get used for selecting fuel ratios along with the TPS. Drop one input, and who knows what's going to happen.

With the TPS disconnected, it would have been dumping a lot more fuel in than the engine needs to run (limp mode). If it idled up and smoothed out, I strongly suspect a very severe vacuum leak somewhere.

As AMDCAMARO said, you really need to pull the codes on the critter, and let us know what it says. It should certainly have one stored about the TPS being out of range in the KOEO test (because you disconnected it with the engine running), and who knows what during KOER, but it may actually pass KOER. I have found that vacuum leaks don't typically set codes on the EEC-IV unless they're so severe that the engine is running extremely lean. This usually leads to people replacing O2 sensors, when the real problem is on the opposite end of the engine. To give you some idea about the O2 input, I disconnected the single HEGO on mine, and had to drive nearly 10 miles before the CEL finally came on. A bad O2 sensor will typically make you get poor mileage after the vehicle is warm because the EEC cannot trim the fuel mixture without it. But, it won't generally affect idle, especially cold idle, because the O2 sensor isn't even in the picture until the engine coolant attains about 165 degrees F. If you have idle issues, the problem will typically be somewhere topside on the engine, be it sticking throttle plates, malfuncting IAC, leaks, whatever. 10 times out of 9, it's a vacuum leak. Get a good vacuum gauge, search in here for vacuum, and you'll find where I've posted over and over about checking for vacuum leaks. Then, have a peek at my gallery, and you'll see the vacuum leak I found. Rough idle may not be caused by external leaks. If the plenum gasket is shot, each cylinder will draw extra air in from adjacent ports on the intake. The fuel mixture is set by the TPS feedback, and vacuum feedback coming off the top of the plenum, where all 8 cylinders have contributed to the existing vacuum. Try to remember, with a V8, on any revolution of the engine, you have two cylinders on intake stroke at the same time. In some cases, if adjacent cylinders, the one farthest ahead in the stroke will rob the other of some of it's air. So, you get one burning lean, and the other burning rich, which balances out in the exhaust where it's metered by the O2 which thinks everything is OK. The truck will cough spit and sputter, but never throw a code at you. (I chased my problem for nearly 6 months of the little spare time I have, and went through a LOT of sensor replacements.)

Oh yeah, one other thing, knowing the model year, engine type (I6 or V8) would help tremendously. Speed density systems work a lot differently from Mass Air Flow systems. This helps us help you. Tell us about your truck, and pull the codes. Use the site that AMDCAMARO pointed to, or www.fordfuelinjection.com. It's easy to do, and you'll get a lot more bang for your buck here.

 

Sorry guys. Motor is a 302W EFI. 89 F150. Has had ALL the usual F truck probs with idle and stalling sometimes due to fluctuating idle. 1st time I unplugged the TPS it went up in RPM and sat steady, but I did it again today and it ran like cr*p so your right old_paint. Have checked for vacumn leaks but cannot find any. Pulling codes is another problem. When I bought the truck, the EEC-V dash light was on all the time when ign. on. Now it doesn't work at all, so if anyone has a wiring diagram for EEC-V light as well as the fuel inertia switch ( cos I've discovered that's missing too and fuel pump runs continually ). Guess mechanic didn't check it enough before I bought it.

 

Your '89 will have EEC-IV, unless Ford Australia did something really weird and jumped into the future. EEC-V wasn't available until 96 or so, possibly later. Some of the Ford Trivia buffs will have to chime in here. '89 was the first year the CEL was wired out. Now, this is assuming you (or the PO) haven't done a MAF conversion with later model electronics. If you have, and you're no longer speed density, umm, you (or the PO) should have added the cab harness for the OBD-II connector too. EEC-V is DEFINITELY OBD-II. OBD-II actually came out with EEC-IV still in use. If you had OBD-II, then, grab a laptop PC, a little software, and you'll have 'er runnin flat out like a lizard drinkin in no time.

But, if you're really still EEC-IV, OBD-I, and Speed Density, all it takes to read the codes is a paper clip, and a small light bulb attached to a wire that can be plugged into the STO pin on the DLC. Crimp a small spade on a socket that will take the small dash lamps (here, Xmas tree lights work dandy, but you're 230V 50hz, so I have no idea if they'll work), Connect the STI (small connector) to SIG RTN pin with the paper clip, one wire with the light on it to the STO pin, and the other wire on the light to the battey + post (might wanna add a fuse as a precaution). Use a small lamp, because something like a tail light will pull the signal down enough it won't be very bright, and you may miss some pulses. Turn on the key, and count the flashes, much the same way as you would the CEL if it were working.

However, if the CEL was always on when you got the truck, this indicates something a little more serious. Are you sure it didn't go off after starting, then come back on? Try the diagnostics test as described on www.fordfuelinjection.com. Some very noticeable things will happen before the codes start flashing. One, you'll hear the fuel pump run twice. Two, you'll hear every output from the EEC pick up one at a time, and it'll sound like a bottle cap fell through the engine bay. Then, the electronics diagnostics begin. If you don't hear the fuel pump run twice and the clicking of all the relays and solenoids, methinks you may have a dead EEC.

Get yer codes, mate, and maybe we can help you get this thing runnin fully sick.

BTW, my better half is Aussie. I'm still pickin up on the slang.

 

Sorry again. EEC-IV. That's what happens when your writing 1/2 asleep. Thanks Old_Paint. Will try and get back to you.

BTW- The utes as beaut as a shrimp on the barbie !
Get your missus to translate that.