Truck:1999 quad cab 4x4 5.9litre gutted cat and k&n cold air kit are its only engine mods.

Situation: On occasion usually at idle but sometimes on hwy the trucks rpm will drop and the truck will really start to run rough almost as if it wants to stall. When you hit the gas it takes a second or two then it will take off and run normal except when you return to idle and tap the gas the engine will continue to rev (around 1500rpm) for a second or two and then return to normal idle. This does not happen all the time.

I have cel on because of an 02sensor but that has been on for a while.

Could be an 02 causing this, or could be the tps? Fuel problem.

I could really use your imput here I wanna figure this out before it leaves me stranded one day.

 

Could be the front o2, or IAC (Idle air control). This doesnt sound like tps at all to me.

What code are you pulling for the o2? if front, replace it, it is likely part of your problem. Rear would indicate either a bad o2, or a clogged/bad cat which could give you issues similar to this.

Take your throttle body off (grab a new TB gasket beforehand), and clean it with carb cleaner till it shines. Make sure to clean the shunt and pintle on the IAC motor, be very careful though, forcing it in or out will ruin it.

 

Cat is gutted. Can a broken after-cat 02sensor produce the described problem?

 

No....I'd be looking REAL hard at the IAC motor. Its free to clean it, and cleaning the TB while your at it is a good idea. First time I did it I was surprised what a difference it made


EDIT: just wanted to mention: Another possibility is the MAP sensor; however, these are known to be very hardy on 2nd gens, and do not fail often. I know 4 people with second gens; all with varying milage and year, and all have the original MAP. They're almost impossible to break, and thus, I strongly believe the IAC is your problem.

 

I will take a look at that tomorrow. It's just a weird coincidence that all of this started happening the day I gutted the cat.

 

Did you smack the front O2 when you were beating up the cat?

 

Trying to remember if the front 02 is reachable with the crow bar I used.

I hope I didn't, how rough can the front 02 cause it to run and why only on occasion?

 

Depends on the failure. There are expensive metals, and ceramic in there, if you manage to just crack it, an intermittent failure is indeed a possibility.

Front O2 is mounted directly into the cat, right where the two pipes come in from the manifolds... so, it is easy to hit..... If it is original, or, has been in there a long time, replacing it on general principles is not out of order.

TPS is another possible though.

 

I thought TPS would be a more constant problem than what he is experiencing(?), and was under the impression that TPS doesnt affect idle that much, which is where his problem seems to like to reside

 

drove 20 mins to work today and it ran like a dream , that being said it will prolly act up on the ride home