A battle I just can't win

[Manarius]

So, I just can't seem to figure out this stumbling issue. If you look in my other thread here you'll see that I replaced my spark plugs and picked up a stumbling and idle hunting issue. I've followed all the suggestions in that thread and even done some of my own and nothing has fixed the problem.

The problem is this: The car stumbles fairly badly when cold. It also can't find idle and stumbles enough to shake the engine. It will also stumble randomly when warm. Seems strong if I am really hard on the gas.

Here's what's been done:
Tested to see if the stumble follows a coil - no response from the car
Replaced fuel filter
Replaced front knock sensor (ECU threw a code - sensor was broken)
Greased all coil boots with dielectric grease
Replaced MAF with known good MAF
Cleaned throttle body with TB cleaner
Cleaned IACV with TB cleaner (emptied about 1/4 of the can into the IACV, made lots of smoke)
Ran Seafoam through gas
Sealed minor exhaust leak

After all that, still no change. I want this stumbling and idle hunting gone. If anyone has anymore suggestions I am open to them. If they involve spending a lot of money, I will probably be a little more hesitant.

[SilverSpear]

IACV... I wonder if that can be cleaned like that and still work properly...

[redlightningsvx]

Did you check to see if you have a vacuum leak?

[michael]

I hate to tell you this but you should undo everything you have done prior to the stumbling. As you undo everything look for what could have gone wrong. If it were me I would start with the connections on the battery and all of the vacuum lines after the TB in addition the seal for the intake to the TB. Check for any cracks in the intake especially the plastic fittings where the vacuum lines connect. Then I would check out the condition of the coil wires and finally check the threading and gap of the plugs. Did you use the right plugs? Are they free of any defects?

[Manarius]

Originally Posted by redlightningsvx

Did you check to see if you have a vacuum leak?

No I did not. However, it doesn't appear that I have one. I can't hear a leak and it goes away slightly as the car gets warmer.

Originally Posted by michael

I hate to tell you this but you should undo everything you have done prior to the stumbling. As you undo everything look for what could have gone wrong. If it were me I would start with the connections on the battery and all of the vacuum lines after the TB in addition the seal for the intake to the TB. Check for any cracks in the intake especially the plastic fittings where the vacuum lines connect. Then I would check out the condition of the coil wires and finally check the threading and gap of the plugs. Did you use the right plugs? Are they free of any defects?

The only thing I did prior to the stumbling was change the plugs and the air filter. The plugs were the recommended NGK ones.

[SVXRide]

Have you tried disconnecting the injectors to see what happens? The seafoam via the gas tank doesn't stand as much a chance of cleaning the injectors as when you connect a line from the vacuum port on the intake directly to the can of seafoam.

can you explain what you mean by "stumble follows a coil"? If you mean you disconnected each coil (one at a time), then I'm confused that you said "no response from car" (i.e., you should hear/feel a drop off of the cylinder when you disconnect a coil). The fact that the car did not stumble before you changed the spark plugs would lead me to put my focus here first (then again, it could just be a coincidence) -- while the plugs may be right, you might find that you've got a cracked insulator on one or more plugs.

-Bill

[kwren]

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[Manarius]

Originally Posted by SVXRide

Have you tried disconnecting the injectors to see what happens? The seafoam via the gas tank doesn't stand as much a chance of cleaning the injectors as when you connect a line from the vacuum port on the intake directly to the can of seafoam.

can you explain what you mean by "stumble follows a coil"? If you mean you disconnected each coil (one at a time), then I'm confused that you said "no response from car" (i.e., you should hear/feel a drop off of the cylinder when you disconnect a coil). The fact that the car did not stumble before you changed the spark plugs would lead me to put my focus here first (then again, it could just be a coincidence) -- while the plugs may be right, you might find that you've got a cracked insulator on one or more plugs.

-Bill

All right. What you described in the first paragraph is what Hocrest asked me to do. While the car is stumbling, he said that I should pull each of the injector plugs to see if pulling one of them doesn't make the car respond. I did this and each time I pulled an injector plug, the engine started missing really badly. This happened with all 6 plugs; which is what I mean in that I tried to narrow it down to a coil but there was no response from the car. Hocrest assumed, and this makes sense, that if you pull the injector plug from the cylinder that's missing already, there should be no change in the engine stumbling. Unfortunately, every injector caused the engine to stumble even worse.

I visually inspected and sealed each of the coils myself in order to stave off insulation issues. You can see a picture in the other thread of what I did to every coil.

[michael]

So one can now assume that it is not a single cylinder causing the problem. You can now either visually check all the vacuum lines or spray them with carb cleaner and listen for a change in your idle. Be careful it's flammable don't spray your exhaust with it! Don't forget to check those connections at the battery as I'm sure those were disturbed during the plug change.

[Mike621]

A similar instance happened when I was installing plugs into my bf's 94 Laguna. I accidentally bumped one of the plugs and closed the gap on one of them, so that the plug was not firing.

However, the test with the coils should pinpoint a problem like that.

[YourConfused]

I found that on mine a similar issue was caused in part by every bolt on the upper half of the intake plenum being loose. I guess that over time they just got that way, but explained the vac leak I was looking for. Other than that I would think that you have a cracked spark plug ceramic, or a voltage leak in the ignition. Brake cleaner can be a fun way to find a vac leak or a spark leak, but is a little dangerous. You can also use propane bottle with a vac hose attached to pinpoint a vac leak. The idle should raise when you find the leaky spot.

[CorSVXette]

I am by no means a mechanic when it comes to these cars( I do work on my 69 Vette though), but when you changed the air filter, maybe you moved something that now has a slight hairline crack in it and it is now letting in air/vacum leak? Just a thought.

[SVXRide]

Originally Posted by Manarius

All right. What you described in the first paragraph is what Hocrest asked me to do. While the car is stumbling, he said that I should pull each of the injector plugs to see if pulling one of them doesn't make the car respond. I did this and each time I pulled an injector plug, the engine started missing really badly. This happened with all 6 plugs; which is what I mean in that I tried to narrow it down to a coil but there was no response from the car. Hocrest assumed, and this makes sense, that if you pull the injector plug from the cylinder that's missing already, there should be no change in the engine stumbling. Unfortunately, every injector caused the engine to stumble even worse.

I visually inspected and sealed each of the coils myself in order to stave off insulation issues. You can see a picture in the other thread of what I did to every coil.

Well, sounds like all of your injectors are working correctly!
If I read your earlier post correctly, the stumble varies with load (?). I'd focus on (1) double checking the plugs to make sure you don't have one that's cracked or has its gap closed up and (2) checking for a vacuum leak (when you "get into it" you're no longer pulling a vaccuum) as you may have bumped a line when you were doing the plugs/changing the air filter.

-Bill

[Manarius]

I checked all the lines today with TB cleaner and spraying each line end to end gave no engine response. However, as the car was stumbling for idle, I thought I could hear a slight air leak and it sounded like it was coming from the EGR valve. I spayed the EGR valve with TB cleaner and the engine didn't respond. So I tried to remove the EGR valve and got stuck because I couldn't remove the tube under it.

I do remember back a few months ago I was pulling codes and the EGR code had been thrown at one point in time, but ever since I reset the ECU, the code has never shown up in my car.

[YourConfused]

Originally Posted by Manarius

I checked all the lines today with TB cleaner and spraying each line end to end gave no engine response. However, as the car was stumbling for idle, I thought I could hear a slight air leak and it sounded like it was coming from the EGR valve. I spayed the EGR valve with TB cleaner and the engine didn't respond. So I tried to remove the EGR valve and got stuck because I couldn't remove the tube under it.

I do remember back a few months ago I was pulling codes and the EGR code had been thrown at one point in time, but ever since I reset the ECU, the code has never shown up in my car.

Well a vac leak can come from a piece of carbon keeping the valve from fully closing. It may be possible that if you reset the ecu with this valve stuck a little open thanks to some debri the ecu will take this as the egr being in the closed position now and no longer will find a fault with it. This car doesn't monitor the flow or pressure of the egr valve to determine if this could be the case. (I may be wrong in this, but would need someone to prove this otherwise.) Just a thought on this.