I bought a 93 XLT recently and I must say I love the Bronco. I bought it and it seemed to be well taken care of and the motor was replaced by ford in 2006 according to the tag on the motor. So here is the problem the truck runs well but has its quirks. When I first had it the idle would scream up to 1800 and eventually fall to 1000rpm or less. For good measure I went ahead and changed the plugs cap and rotor with stock components. I went through the vacume lines and replaced everything that was questionable. The Coil is a MSD brand for informational purposes. After the swap out the truck did the same things so I went ahead and pulled the IAC valve for cleaning along with the throttle body.(throttle body said do not clean) They however were both so filthy I decided to clean anyway. After the cleaning IAC and TB the truck ran smooth and the idle was down to 600-700 from a cold start. I don't believe this is right however. The injection system went from running high to low from the start. Additionally I have noticed that there is a skip from time to time and if the truck is put in or out of gear. It will occassionally stall when shifted. Once started up again the truck will run fine and may even stop the skipping at idle. The drivability however is good and she rolls down the road with power and not skipping. Before spending the bucks on a factory IAC I want to here from the ones with knowledge. My truck is not setting off any codes. The motor is a 5.0 with shorty headers with O2 attached. The intake is coupled to a K&N air filter kit. Other then these items the motor is stock. Any suggestions?

 

Welcome to FTE and the Big Bronco Forum. We will do our best to get you the most accurate information we can.

No codes? At all? Impossible.

However, cleaning the IAC, as you did the throttle body, is a good idea either way. Just don't use anything but cleaners that are safe for "sealed throttle bodies" and catalytic converters. The IAC consists of a mechanical plunger-type valve and a solenoid. Keep liquids of ALL kinds AWAY from the solenoid end of the assembly. Take care when cleaning to NOT use anything abrasive as this will cause the valve to not seat properly and the by-pass airways to become bigger than they should be. a good soak in some mild parts cleaner and the crud should wipe right out of it.

 

Thanks for the info. When I took the parts off I used b12 to clean the parts. I disassembled the iac valve and cleaned it. I used no abrasive materials to be safe. As far as the codes are concerned, I will need to pull them. The check engine light is not on nor has it ever come on.
The skipping issue is something that is annoying and was wondering if changing my firing order may fix my problem. I heard crossfire leakage was a problem in 93 and this is why the firing order was modified in 94. Thoughts?

 

The check engine light doesn't come on as often as you think. I can throw a dozen codes without seeing a check engine or any other kind of light, all which effect drivability. Everything from EGR to my IAC were throwing codes at some point with no check engine light.

Check codes, trust us.

 

Thanks for the message. I will check the codes later today to see what I am up against. Appreciate the direction and help. Ill let you know what I come up with.

 

Erros is right. The codes that trigger the CEL are usually something that is detrimental enough to performance to cause potential damage if left unchecked. Best case scenario you get ONLY Code 11 or 111. This would be the "system pass" Code indicating that the computer has seen no faults during the test(s).

Once you have Codes, let us know. There are Codes that, when triggered, will cause other Codes to be generated as well. There are "shortcuts" if you will, to getting multiple Codes dealt with but only performing the fix for the most critical. Unfortunately I can't give you a method for this part... it comes with experience.

 

i was almost certain cleaning or replacing the IAC would do the job because that controls the idle when in gear. if its not working it acts like a cold dirty carburetor.

after 10 minutes of engine idle, pull the plug on the IAC and see what happens.

i would also check voltage of the TPS circuit for the 5v variance. it is worth replacing while you have the throttle body off next time you clean the throttle body

 

If you do pull the IAC connector make certain you clear the code generated when you do. Otherwise, even if you fix the problem, the computer will have a stored IAC fault code that it will try to compensate for. Removing the IAC connector really only serves one purpose. It will tell you if you have a vacuum leak or if the throttle plate stop screw has been messed with. You don't want either of these things to be the case. so unless the engines dies shortly after pulling the IAC electrical connection, you have either vacuum leak(s) or someone monkey'd with the throttle plate stop screw.

 

Thanks everyone. I broke out my auto xray and did some test and I discovered a few codes and I hope I can get this sorted without too much pain. The codes were these after erasing the initial set. Greystreak I know the throttle plate was monkeyed with at one time but not sure what the procedure is to get it back to factory settings. The codes I tripped are the following:
KOEO Fast
121 TPS/Pedal position out of range
334 EVP Sensor closed valve above max range
111 system ok
565 cannister purge sol ckt malfunction self test

KOER Fast were the following
412 Cannot control RPM during self test RPM CHeck
121 TPS out of range
538 insufficient RPM Change during self test

Based on my evaluation I think I am looking at a new IAC and either new TPS or resync of the TPS. I believe this is possible but not sure. The evap sol fault looks like a bad selenoid but I am not sure on that one. Thanks for all the help here.

 

Well I replaced the IAC with a genuine ford(installed a new gasket) one and my idle went to the roof. Not sure why this happened but want the opinion of others. I continue to receive a TPS out of range fault but I question if that is the reason for the high idle. All my vacume lines are new and I see no apparent leaks. If I disconnect the IAC the idle comes down to sub 800rpm. I a little perplexed. When I clear the codes and plug the IAC in the engine returns to high idle.
On another note, the previous owner installed a KN filter and the MAF sensor is now missing. Would the lack of this cause the PCM to tell the IAC to add air to drive up the idle?
Any help would be appreciated.

 

Sounds like it's the TPS to me.. TPS is used to control air-fuel throughout all ranges, even idle WITH the IAC. IAC doesn't control the idle completely, TPS helps with it. Usually that "cannot control RPMS" means the TPS is bad.

A vacuum leak or IAC should not cause TPS codes. I'm sorry I didn't see your last post from the 26th..

edit: If someone screwed with your idle stop screw that might have something to do with it as well, but I don't think that would cause you to throw a KOEO TPS code

 

About the K&N and the missing MAF sensor, its possible that your bronco is a speed density system and may have never come with a MAF sensor. I have a 95 and have looked into installing a K&N air filter. There are 2 options, one for those that have MAF, and another option for those with Speed Density (not having a MAF). I disconnected the connector on my MAF and it wouldnt stay idleing unless I stepped on the gas a bit.

 

I'm very positive that since his truck is a 93 it isn't a MAF, it will probably have a SD system. My money is on the TPS right now, i'm having the same condition right now (the truck stalling out if i brake too fast, also stalling when i try to back out), i'll try some corrective measures soon and will let you know the results.

 

Thanks for the input. 1993 seems to be a oddball year for the truck. I will check and test the TPS before buying one. As for the throttle plate, there was someone who monkeyed with it. I have it set to be off the screw right now so the plate is closed at idle. If I clear the computer I still get the TPS fault. I didnt think much of it since the motor revs fine. I will check it and adjust it if possible. I have the manuals but see nothing on the throttle plate for proper setting. More to follow after I test. Thanks

 

Yup, replace TP sensor, clear codes, retest with the engine at op. temp.

There are no factory MAF 93's. Very late 94's maybe. What you disconnected was the IAC (Idle Air Control) solenoid. Clear the codes before you run the truck again because disconnecting it stores fault Code 412 which is why it showed up in the KOER test.

Code 334 - triggers if the vacuum line to the EGR valve gets disconnected at some point in time while the engine is running. If you have no performance issues, I'd clear it and see if ti comes back.

Code 565 - is the same situation as above but runs the canister purge solenoid OR the solenoid is disconnected/failed.

Code 538 - is an operator error wherein the "goose test" did not maintain the minimum 2000rpm for the duration of the dynamic response portion of the KOER.

To reset the throttle plate stop screw correctly:

1) Warm the truck to normal operating temp.
2) Shut it down and make sure you can access the IAC connector easily and safely with the engine running.
3) Start the truck
4) Disconnect the IAC at the connector.

- the engine SHOULD spin down and die within seconds.

5a) If it does, turn the key off, clear Codes, reconnect the IAC and leave everything the way it is.
5b) If it does NOT, turn the key off, back the throttle plate stop screw out until the throttle butterflies are JUST closed in the bores, clear Codes and repeat steps 3, 4 and 5b until you get the result you need.

CRITICAL NOTE: This procedure WILL NOT WORK if there are ANY vacuum leaks. Period!