Strange start up idle, intermittent engine cutoff...

[Canndspam]

I have an '86 2.9L ranger. Typically, when first started cold, it revs high and then drops to its normal idle speed. Recently, when i start it up in the mornings, it has been idling low to the point where it almost cuts off and then revs high, as if to keep itself going and repeats this cycle between 5 and 10 times before it returns to it normal idle. In addition it has occasionally cut off while coasting while driving. Once it cut itself off when I was accelerating onto the highway. When this has happened I have been able to pop it into neutral and restart it immediately. I extracted the codes from it and it read that the egr valve position sensor was reading below minimum voltage, so i replaced said sensor. Now it is throwing codes saying that the egr valve is not opening (which i could care less about) and that the hego sensors say that the engine is running lean. I'm not sure where to go from here. The engine hasn't cut off in the last three days since I replaced the EVP sensor but the startup idle is still strange. Any recommendations?

 

[jhammel85]

They could be causing a domino effect. Like one is effecting the other...Did you happen to clear all of the codes?

Since it sounds like all of this is started with the EGR, it might be as easy as swapping in an 88-92 ECU. They ignore the EGR components since they were not used after '87. I swapped one in mine and it's so much better.

Other than that, I would check the wiring around the area. Maybe even on the oxy sensor (even thought it does seem like its working)

I actually have the same problem with the start ups. My truck runs extremely rich when it happens. It smells like fuel and sometimes I even get a very small puff of black smoke when it happens. The fuel pressure is always where it should be and spark seems OK. I checked to see if anything was missing while using a timing light on each wire. All of these things you may want to check your self.

It seems to be some what common but I have yet to find a definitive answer on it..

Good luck!

 

[Duane867]

No IAC code ?

 

[Protowrxs]

No IAC code ?

My guess as well.

I have had rough idle /stall / super rich / gas in the oil from a missing MAP sensor though on the one we just rescued.

 

[Canndspam]

When I first ran the codes it threw 41 (HEGO indicates system lean), 31 (EVP below min. voltage), 25 (knock sensor not tested), and 74 (brakes not tested). I cleared the codes and installed the new EVP sensor and ran the self test again and got codes 41, 33 (EGR opening not detected), and 74. Nothing mentioning the idle air or MAP. I've listened, tube in ear, for vacuum leaks and checked for bad wiring on sensors but nothing apparently wrong on those fronts. I replaced the computer about 9 months ago so I'm a bit reluctant to get another, but, Jhammel85, if you say its so much better I might consider it. It seems to be running alright since I changed the EVP with the exception of the weird start idle, though it has only been 3 days. I haven't noticed a decrease in gas mileage, though I haven't actually checked accurately. Should I try taking out and testing individual sensors? Should I just accept the fact that I have a 25 year old truck that's bound to run a little funny at times? Thanks for your help thus far guys...

 

[Duane867]

I would clean your IAC.

 

[mendozamm]

i had a 88 2.9 do something similar. Change IAC, MAP and nothing. Eventually it started stalling when I started it up in the mornings. I guess when the engine was cooled off, it would start up and die. idle went up and down till it died. it took me like 5 - 10 min every morning to get it going. but she was fine the rest of the day. Then coming home she started to do tps symptoms. waited for it to cool off. but it never started up again. Figured out it was my pickup coil inside my dizzy. swapped it out with a new one. She running good!!!

 

[06RangerXLT]

The egr not opening can cause a running rich situation. Normally the egr will not only lean out the gas because some fuel is recycled, but it also warms the engine up faster. I'd replace what's not working, before buying parts you don't know if you need.

 

[Canndspam]

Sorry to resurrect a dead thread but i realized i never posted the solution. In the end what completely solved the problem was replacing the egr valve and the o2 sensor. the o2 was giving a false lean reading and causing the engine to run rich as well as other weirdness compounded by the non functioning egr, which i found was totally clogged with soot.