My 98 4x4 acting a little strange, when I start the engine it revs up to 2200 rpm and droppes to around 900 when it is warm.

It also surges a little when it is running, about 200 rpms?

I have checked all the vacuumlines and sprayed them with brakecleaner and could not find anything on the TB.( I have a KB SC so all the lines are hooked under the TB now).

There are three vacuumlines under the TB : 1 for the PCV valve, 1 for the Brakebooster and 1 to the cruise control wich also goes in the car I think for the airco and stuff.

On the TB there is just 1, the 1 for the EVAP, the one for the MAP is plugged off and the line for the MAP is coming from the Kegger.

The evap valve on the driverside I have not checked, becuase I do not now how to check it, or I must plug the line that goes to the valve, and iff there is no line or the line is broken after the EVAP is that a problem?

I have replaced the TPS and the IAC, reste the PCM ( battery of for half hour and trned the key to start position with the battery disconnected).

When I start the engine now stills revs it up to 2200 and the dies.

I have taken the IAC off againn set the plunger total out and put it back and start again.

I will not idle now but no more reving to 2200 and I must put the pedal a little down to let the engine start.

There are two O2, in my truck, one before and one after the cat (gutted), the one after has a O2 sim on it, the first I have replaced 35.000 miles ago.

What can be wrong?

I will put a video with this thread the battery from my phone is empty....

I hope some has the solution for me......


Thanks and greetings,


Erik

 

my experience has been that surging idle was usually the TPS. failure to idle at all was usually clogged up IAC well, or bad IAC.

trying unplugging IAC and see if you get a different result, or sound. if the IAC is working it should be moving the plunger/pintle thingy in/out in an attempt to keep it running. this might be visible whien looking down the TB with air filter off. i don't recall if you can see it or not. movement of the iac usually produces a sucking or whistling sound.

if you can keep it running by opening the throttle plates just a little, or by moving the IAC out of the well just a little, then its likely a bad IAC, but check the port first, as it can get clogged with gunk.

you should not pull, push, twist, or even look directly at the IAC pintle. it seems to be a fragile little thing.

 

Thanks for the reply,

As I said when i removed the connector and tried to start it I must put the pedal a little down and then it start normal.

I have used the old IAC to push it out, byt with the old and the new one there is no difference.

With the IAC disconnected I have set the idel at 900, in drive its is 700, and the engine keeps idling without surging.

So it seems that there is something sending the wrong signals to the IAC?

I will post the vid right now.

Thanks and greetings,


Erik

 

Here is the vid :

 

Evap purge selnoid on the driver side back of the engine, it should have atleast two or more vacume lines coming out of it with a electronic plug ontop or bottom.

Its different in between years, take that off and disconnect the hoses, if you can blow through the inlet in either direction then its bad an needs to be replaced, thats whats wrong with mine right now and iv got the part on order.

 

Thanks for the answer, I will check that!

What is the the inlet?

The bottom goes to the TB, th eother side to the line that goes under the truck.

Thanks and greetings,


Erik.

 

the one that goes under the truck is the one that goes to the transfer case i do believe, you shouldnt be able to have any blow through on either one, IE blow on the top one and if air comes out the bottom one it needs to be replaced, also if you tap on it a little bit and any carbon pellets falll out then thats also a damn good sign it's clogged and needs to be replaced.

 

Thanks I will try!

What happens (to test only) if I blocked the vacuumline between the EVAP Solenoid and the TB?

What happens when the line is leaking before the solenoid(the line that goes under the truck)?

Thanks and greetings,

Erik

 

Not real sure to be honest with you, i personally would think if you plugged them both it would run smoother considering its not leaking.

I havent tried, i also have another vacume leak im working on tracking down, called wild vents.

 

Wild vents???