I have this headache of a problem with my motor. I took a video and posted it on youtube. For some reason whenever I start it, it starts to stall then the computer brings the rpms up to about 2500 and then lets it drop, and repeats until the idle finally bounces between 1100 and 1400.
When I put it in gear, the it will idle down the road just fine, but if you touch the gas pedal, it wants to die and back fires. If anyone has any ideas I would GREATLY appreciate it.

In the video I unplug the EGR solenoid and then plus it in. Then I unplug the vacuum line going to the EGR valve and the idle keeps doing what it is doing. If anyone has any suggestions I will make more videos and repost results.



Will

 

Three things I would check

1) Fuel pressure - should be between 9 to 13 PSI. In high millage cars and trucks in tank fuel pump outlet hose develops a leak. This is very common problem.
2) Base timing - check your emission label. Timing is set with EST plug open. There is a timing procedure posted in the technical stickies.
3) EGR valve passage and EGR valve diaphragm. Make sure that EGR is not stuck open. At idle, and stationary EGR valve should not be letting exhaust gases into intake.

//RF

 

Hey thanks for you help. I posted a video on my youtube channel with a fuel pressure gauge hooked up to the supply line. I had a steady 12psi. So I thought I had enough fuel pressure. A couple days later I realized that I could just be pumping it around in a circle and the actual engine was not getting the right pressure. Started it up today and pinched off the return line with needle nose pliers to raise the back pressure. Straightened out and idled nicely for a cold start. The idle even started coming down as I held it there. Then I let go of the return line and the surge came back. Did this 4-5 times to confirm. Now I am in the market for a fuel pressure regulator.
Will

 

Ok, I was wrong. Put the new adjustable fuel pressure regulator on and got the pressure up to 14psi. Helped the first time I ran it, but the second time the surge was just like it was. I made a video of me pinching the return line and straightening out the idle while opening the throttle, but there is a hesitation and it pops back through the intake (lean condition). Also the fuel pressure was around 18psi. Any info would be helpful.
Will

 

Did you check base timing????

Surging idle in original appears as a huge vacuum leak. Check all hoses, makes sure there is no cracks. I would check all vacuum ports - look for a vacuum leak using carb spray. Old TB to intake gasket can cause a huge vacuum leak and will sound like whistle.

On rare occasions exhaust system develops a leak allowing extra oxygen before O2 sensor. This is a problem in vehicles equipped with AIR system and air pump. A stuck or malfunctioning check valve will allow extra oxygen into exhaust. ECM will try to compensate resulting in unstable idle. Check your exhaust system for leaks.

//RF

 

Thanks for the info. I did set the base timing, as per the instructions that it be set at 0 degrees TDC on the number 1 cylinder.

I have been looking for vacuum leaks for months now. All the plastic hoses seem in great shape. I assume it has to be a huge leak to make it surge that much. I am going to take a closer look at the brake boaster and the PCV tomorrow. I have sprayed the TB/intake gasket before with no change in idle. I think tomorrow I will be more aggressive with that.

I have checked the EGR, I took it off, tested it and it worked fine. Cleaned it anyway and reinstalled it.

Tonight I tested the TPS and it passed all the specs according to the manual. I also tested the ECT sensor and its specs were all within range.

I haven't tested the IAC yet mainly cause i'm not sure how.

I also haven't looked at the exhaust yet. That has been redone after this problem has started. Everything but the exhaust manifolds.

Why is it when you increase the fuel pressure the idle straightens out?

I also took another video today which I will be uploading to the youtube site momentarily.

Thank you for your help.
Will

 

I added a few more videos testing different things. Creating vacuum leaks (interesting results).

https://www.youtube.com/user/ironwill04


Will

 

Will

Took a look at couple of your Youtube videos. In the Video that shows injector it is appears that it is dribbling fuel. It should be a fine mist at idle, no large droplets! I am going to send IM with a link to video.

//RF