Surging Engine

The engine in my Truck surges and when i stop it dipps below 500 and then catches. i know this is a bronco forum but you guys help alot. any ideas? its a 94 f-150 with a 5.0 in it

KansasBronco said:

The engine in my Truck surges and when i stop it dipps below 500 and then catches. i know this is a bronco forum but you guys help alot. any ideas? its a 94 f-150 with a 5.0 in it

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a vacuum leak could cause a surging idle.

Does the check engine light come on?

no it does not.

KansasBronco said:

no it does not.

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This thread says it could be your Throttle position sensor

http://broncozone.com/forums/index.php?showtopic=13404

another thread speaks of it possibly being a vacuum leak.

a member here "Jersey" spoke of how to check for vacuum leaks with a can of carb cleaner you can search for it.

Others mentioned listening for it with a mechanic's stethosocpe, or a cardboard tube from a paper towel roll or gift wrap roll.

Does the truck run fine otherwise?

When was the last time you gave it a tuneup?

I would say it is a vaccum leak. My 86 5.0 does the same and I know it has a vacccum leak that I have to fix. I alos know that it didn't act up until I got the vaccum leak in it.

it runs fine otherwise. and when i looked at the vacuum lines, i pulled one off and didnt feel any type of suction. so that might be it. ill try that and the tps. thanks!

KansasBronco said:

it runs fine otherwise. and when i looked at the vacuum lines, i pulled one off and didnt feel any type of suction. so that might be it. ill try that and the tps. thanks!

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You're welcome. I hope it works out for you, Please post us and let us know. I get a personal satisfaction in knowing that I helped, and others with similar problems will like to know if it worked.

IF that wasn't it, let us know. There are a number of guys here who much more knowledgeable than me and are willing to help do troubleshooting.

Good luck

joe

could be a vaccume leak, could be your TPS, could be a dirty or clogged up throttle body, check all of those out

Yeah I know what your going though.... It sucks... My truck stalls when I pull into a parking spot (using your brakes puts a vaccum load on your engine plus turning your wheels puts a load on the power steering pump) but it drops real low idle then I just stop at a light or stop sign( only has the load of the brakes). Well when I rebuilt my engine I replaced every vacuum line. Well... I still have it, even with a new TPS, New vacuum lines, oxygen sensor, knock sensor, coolant sensor, distributor, cap, rotor, wires and plugs... All replaced while I rebuilt it, no fix. Well the only things left are the MAP sensor and the IAC valve or commonly called the bypass valve because it allows air to BYPASS the butterfly valves of the thottle body. It is a small electric motor that opens and closes to controll the idle of the engine. This is what I expect to be the problem. Like all electric motors it gets sluggish with age so it would explain the idle surge as it tries to adjust idle (it stalls when I first start the engine in the morning so I have to give it a little throttle for a minute or two to get it started. I had to do before the rebuild also). The valve is no longer needed when I use the throttle so I have no problem once I'm driving. I have not replaced it because it ain't broke and its $60. It could possibly be the MAP sensor but I don't know much of that other than I THINK it tells the engine the Barometric pressure so it can mix the fuel and air more efficiently. Well all info has a price so if you read this you are obligated to left me know if you replaced it and if it worked. So good luck bud...

PS... If you pull the plug off the valve while the truck is running and at idle it will stall. That will tell you that is works or is working but my theory is that it is not working as WELL as it should to keep the truck running smooth... You should pay attention if you problem happens when you (1) left your foot off the throttle and/or (2) when you go from park to drive and back. Also I found that if you tap the throttle real quick the idle will instead of rising, will drop and cause the engine to surge as if its searching for idle again. Then it will either steady out or stall. Mine does one or the other when it feels like it.

i cannot for the life of me find the map sensor in my truck... anyone know where it is????

KansasBronco said:

i cannot for the life of me find the map sensor in my truck... anyone know where it is????

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on my '90 it is on the firewall on the passenger side.

It has a vacuum hose coming off of it.

BroncoJoe19 said:

on my '90 it is on the firewall on the passenger side.It has a vacuum hose coming off of it.

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Here is a picture of one.

i will check it in a bit! thanks!

i just asked the ford house and i dont have a map sensor. imagine that... but i did replace the tps and now its acting worse... any ideas? and now its putting out a check engine light..

make sure your tps is on the right way... i have a 93 5.0 and when i first put on the new tps i put it on wrong :/ go figure. check engine lite and all. ran worse. i took it off and put it back on the right way. and it was fine. just take a look at it. my bronco has the same problem, stalling out when there is a load on the engine. i almost think its the air pump, as i have replaced almost every sensor. just maybe the air pump is not holdin up as good as it should?

Hmmm, IF you don't haave a MAP sensor, then I guess you have a MAF setup.

It is my understanding that a MAF has a filament than can get dirty, and may cause your problems.

OTOH... As stated above. it could be a vacuum leak, and if it has gotten worse, then it may be easier to find.

Also... now that it has gotten worse, it is throwing a code... good for you!!!

Check your codes and lets see where that takes us.

joe

alright. i replaced the air bypass or the IAC valve and the TPS and it fixed the problem! Thanks guys for your help!!!

KansasBronco said:

alright. i replaced the air bypass or the IAC valve and the TPS and it fixed the problem! Thanks guys for your help!!!

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Yahoo!!!

I'm glad you got it working. THanks for letting us know what finally fixed it!

Now you can get out and really enjoy her.

joe

I'm glad you fixed it, i guess i'll spend the $60 get mine running right. Im currently in the middle east serving as a C-5 mechanic for the US Air Force. I'll be home in April, back to my baby (my truck)... and my wife and daughter. Well have a good one.