engine surging

[therover87]

i have an 87 k5 blazer and i cant seem to fix the problem of the engine surging, its fine when i first start it and when it warms up is when it happens, i changed the o2 sensor, plugs, wires, cap, coil, rotor, egr valve, could it be a vacuum leak and if so how do i check for that, also should i buy a idle air control valve? or i shouldnt even bother, thanks

 

[ftn96]

having the same problem

 

[Stoopalini]

Your '87, if it's stock, should be a TBI engine. When it first starts up, the computer (ECM) runs in Open Loop mode. When the engine warms up, the ECM switches to Closed Loop mode and starts reading from all of the sensors and makes appropriate adjustments.

If your getting surging after warm up, you probably do have a vacuum leak. Get a can of starter fluid, and after the truck is warmed up, spray the starter fluid in small bursts around vacuum lines and also the TBI/intake seal. If one of them is leaking, the engine will rev up to a higher RPM when you spray it.

Good luck,

Thomas.

 

[ftn96]

After reading stoop's response I re-read your post and compared them to my situation and it led me to ask you if you would define your definition of surging?

Mine is more like a not running right to spudder then take off only for 1/2 second or so then back to crappy (back and fortherratically) only until I floor it and get the RPM's up over 2000 or so. I guess from the downside looking up that could be surging. I've replaced everything under the hood just short of the EGR (+/- control solenoid), Throttle pos. sensor, coolant sensor and the MAP.

 

[DesertDueler]

Change your IAC motor. mine did that until I changed it.

 

[wheelnut46]

How's your fuel pump? Had a problem similar to that in an old GMC pickup a few years back, replaced the fuel pump and fuel filter and the problem disapeared.

 

[ftn96]

been there done that. It sounds like to me that any one of the emissions gadgets can cause this problem, just finding out which pertains to each situation is the hard part.

 

[HuskerBlazer]

Try the Coolant Sensor. Mine wouldn't idle worth a crap when cold, and I had to keep the revs up at about 2000, but was fine when it was warmed up. Changed the ECT, and cleaned the IAC really well. No probs since (*crossing fingers now*).

 

[ftn96]

But mine is doing just the opposite. Its fine when cold and running like crap when its warm.

 

[Thunder]

FYI
Its far <font color=red>Safer</font color=red> to spray water out of a spray bottle on your hoses, gaskets ect when checking for a vacume leak than flamable liquids. You use it the same way. But with water the engine RPM decreases when you hit the vacume leak. And there is no danger of fire.

Also
It really helps to have a good scan tool like an Autoxray when chasing problems like these. It will save you money in the long run. Replacing sensors till its fixed can get pretty expensive.
Autoxrays are around 130 -150 bucks. A couple of sensors needlesly replaced can cost that much. Mine has saved me a lot of time and money.
As stated in posts above Surging can be caused by Vacume leaks, A bad IAC or EGR problems. A scanner, when used properly will tell you pretty much where to find the problem.

 

[HuskerBlazer]

Damn got crosse dup on your post. Still coolant temp sensor recognizes both cold and hot...if its out or screwy, it sending bad signals back to the computer. Bad signals=bad idle. Couldn't hurt to clean the IAC as well. Tends to build up a lot of carbon and gunk especially when not a lot of hiway driving.