Odd Idle Issue 1987 b2000

Hello everyone! My name is Kori and I am desperate for advice, I have a 1987 b2000 that I love very much and it is having the strangest issue and I am open to suggestions or advice based on past experiences. Back in November I was driving to work and out of nowhere the truck starts to idle very rough and tries to die. I pulled over to check spark plug connections and everything was fine, I started to pull wires to see if there was a change and when i pulled 2,3,4 it ran worse, but when I pulled the number one plug it ran better! since then here is a list of things I have changed since then to try and fix the issue:

Carburetor (installed a weber 32/36)
camshaft
spark plugs/wires/distributor/ignition coil
took the head off and had it machined ( the cylinder walls looked good and I changed all the gaskets, hoses, and belts along the way)

It is still giving me this very odd issue, and I am at a loss of where to go from here. The truck still runs and drives and doesn't overheat and there is no mixing of fluids. I am so sorry for the long post but I really want to get this fixed

"My name is Kori"

Ha !!! My youngest daughter's name is Kori !!!


OK, back on subject. Does your truck still have its EGR valve (on intake manifold on passenger side of the engine) ??? A stuck-open, or partially stuck open EGR can cause rough idling and stalling. With your Weber, you don't even need an EGR on your truck (I have a Weber like yours, and made a block-off plate for mine).

I doubt that the Weber primary or secondary idle jets are clogged, which could also cause such issue, because yours is so new. Could you have vacuum leak with your new Weber, pretty common. Did you make sure the adapters for the Weber were PERFECTLY flat by wet-sanding on a sheet of glass, and using brown Permatex Aviation on the gasket surfaces?

Ha thats awesome, very rarely do I meet another girl named Kori let alone with the same spelling! It does still have the EGR valve, I was going to rip it off and make a plate soon, hopefully this weekend. i will also run it without any exhaust on it to see if it is possibly some weird issue based in the manifold or catalytic converter. And I did, we polished it really really well and clean it with acetone, and used high temp gasket sealer with the provided gaskets. Thank you for the response!

If you haven't invested in a vacuum gauge yet now might be a good time to do so. It wasn't clear to me weather you had replaced just the distributor cap or the whole distributor. A bad vacuum capsule on the distributor might cause some of what you are describing. Something that is easily overlooked is a fuel filter. That can cause an erratic idle. You can try spraying some carb cleaner near the gaskets or hoses and see if the idle quality changes. The brake booster line is bad about partially burning through at where it connects to the intake manifold and that can cause an idle problem. Hope that helps.

The EGR valve itself - if fully closed -can also serve as its block off, just plug the vacuum line to it and disconnect the little harness. Frequently these EGR valves crud up with hard carbon and get stuck, did happen on mine.

There are a zillion vacuum ports that must be plugged. I've found vacuum caps other than factory to get brittle and crack after just a few months, I use pieces of vacuum tubing and wood golf tees to block off. A vacuum leak can cause poor idle, but not be too noticeable at higher rpm.

When my daughter Kori was 5 and playing T ball, the coach would have their names on their hats, ready for them 1st day. Well, on a team of about 13 and 2 or 3 gals, there were two named "Kori".

Thanks for the response guys!
I did replace the brake boost line, as well as all the vacuum lines and capped off all the ones no longer needed, and it is still happening.
I also replaced the distributor, because I thought it was a faulty vacuum advance that was causing the issue and no change. :/
I am starting to think that there is either a crack in the intake manifold (replaced the gasket when I took the head off) or that possibly there is an issue still in the valve train that the machine shop missed when the head was re-machined?

I dont think its the fuel filter? just because im not sure how that would make the idle jump up on cylinder 1 when the spark plug is pulled, but not the others. I will replace the fuel filter this weekend though, just to cover that base too!

See http://www.mazdatrucking.com/B2200/B22TimeCheck.html and check ignition timing and order of spark plug wires on distributor.

I doubt the fuel filter is involved because the issue is more pronounced at idle than at higher speed/higher rpm.

I thought about your issues some more, and based on what you have said I am going to suggest that you do some things. From what you described, the engine runs smoother when cylinder #1 is disconnected. The only thing you notice is that the idle gets lumpier when you add #1. That indicates that there is an imbalance between power strokes between cylinders 1-4 when #1 is added in. I don't know if a compression test would be helpful, but it wouldn't hurt. Cylinders 2-3 are cancelling each out while 1-4 are fighting with each other when both are connected. I think a wet compression test will demonstrate that cylinder #1 is low and not compressing the mixture as well as cylinders 2-3-4. The cylinders should be between 20% of each other. The other test can be done with an ocilloscope, where a cylinder balance test could be done. They would test for firing voltage against each of the four cylinders. A low firing voltage would indicate a lower compression in a cylinder.

Spark plugs/wires are all in order, I have checked, and double checked, and since we have put a new head on with a new timing belt it was re-timed with a new belt (initially we though it had skipped a tooth)

I will do another compression test tomorrow though, initially I did one before I sent the head off and they were all consistently low ( all in the 110 range). I was hoping that having the head machined would fix the issue but it didn't :/