If you can solve this problem you're my hero!

[SuperRA]

Maybe I'll even consider paying you...

91 4AFE Sedan

Problem: When it warms up after a few minutes, a misfire at idle shows up. At maybe 1500 to 2000 RPM it goes away. I can feel the exhaust pulses at idle and 1500 and it definitely smooths out.

What I've found out: I'm pretty sure it's a particular misfire and not random. Listening to the exhaust you hear a steady rhythm of misfire. At 1500 I hear and feel no misfire. (putting hand upto exhaust tip). Also, I've unplugged the injector on cyl 1 and found no noticeable difference in bad idle while unplugging other injectors do make idle even worse. I've also done this with the spark plug wires and got the same result, cyl 1 didn't make it worse, while the others did. So I'm 98% sure the misfire is in cyl #1.

I also know the injector is working because I've swapped it with cyl 2 and the problem stayed at cyl 1. Also when I rev it steady at 1500 (where misfire disappears) and then unplug injector #1, the engine gets worse. I've also swapped it with another used injector and the misfire persisted.

I can see spark getting to the #1 plug wire when I take it off the plug, it will spark to ground. What I can't see is if the spark plug itself is sparking, but it must be sparking at 1500rpm because it runs smooth there.

What's been changed:
-Cap/Rotor
-plug wires to a good used set. (both old and current sets check out good resistance wise)
-EGR valve (used)
-spark plugs (new)

I've checked:
-MAP sensor
-TPS
-Swapped ECU for another used one
-Coolant temp sensor
-Air temp sensor
-Compression (~180psi in all cylinders)
-Opened valve cover to see that the cam does push down the lifters/valves
-Coil resistance was a little off but since plug wire #1 gets spark, ignition should be good
-Distributor pickup gap (again, spark gets to plug wire #1 so ignition is good)
-Cold start injector is not leaking
-Fuel return is not clogged
-O2 sensor checked according to the FSM (swinging voltmeter needle method)

I haven't checked:
-Ignition Timing (I don't have a timing light yet) but could timing really affect only one cylinder?
-Timing belt timing (doubt this is the problem)

Sorry for the long post, I tried not to forget anything I've done and all the details.
It's been real frustrating and I want to just rip the engine out.

[90 GP]

Did you check the valve clearance for out of spec on cylinder 1? Did you check for stored codes that may be present but not triggering check engine light? A long shot could be a slight coolant leak into cylinder . A dud distrib cap/rotor (particularly if aftermarket) even though they are new. Try swapping another spark plug on cylinder 1.

http://www.troublecodes.net/Toyota/

[Flashmn]

You did a compression check, but do a leakdown test too.

[heartdisease]

Sounds like a little oil fouling and it burns off at higher rpm? Maybe try a little hotter plug in that cyl?

[Tech1984]

You really need to get that timing checked. Also check the advance movement, Stuck centrifugal weights can cause this. Edit: never mind that, you have ESA for your advance.
How just #1 is affected I can't explain at this time. Possible HC/CO being off a little in that cylinder. ie: vacuum leak at #1 intake runner?
Checking the basics first usually fixes the problem.

[toyotaspeed90]

it's possible that it could still be the coil.... the 4afe has an epoxy coil.... if it has a hot spot on it then it could be creating a weak spark that is more noticeable on a specific cylinder. They can also build up moisture and cause problems.

were the issues present both before and after changing the plugs, wires, cap and rotor?

[SuperRA]

I forgot the mention that the problem existed before changing any parts. The problem was the reason for me to work on the car. So I'm pretty sure none of the new parts are causing the problem.

Originally Posted by 90 GP

Did you check the valve clearance for out of spec on cylinder 1? Did you check for stored codes that may be present but not triggering check engine light? A long shot could be a slight coolant leak into cylinder . A dud distrib cap/rotor (particularly if aftermarket) even though they are new. Try swapping another spark plug on cylinder 1.

Valve clearance? Is that the clearance between the lifter shim and the cam lobe? That I did not. I only checked to see if something was majorly wrong which it did not seem to be. I did forget to mention that the ECU finally lit up the check engine light. I gave me codes #25 and #26 which is engine lean and engine rich. (Gee thanks alot ECU, that helps... lol) I did try checking all the parts that the FSM suggested for these codes.

Originally Posted by Flashmn

You did a compression check, but do a leakdown test too.

No I did not. I don't have the tools to do so. Maybe as a last resort.

Originally Posted by Tech1984

Possible HC/CO being off a little in that cylinder. ie: vacuum leak at #1 intake runner?

I considered this and tried spraying near the intake and head mating surface. Didn't notice anything different. The exhaust smells and feels really rich so I didn't think a vacuum leak (lean condition?) was causing this.

Originally Posted by toyotaspeed90

it's possible that it could still be the coil.... the 4afe has an epoxy coil.... if it has a hot spot on it then it could be creating a weak spark that is more noticeable on a specific cylinder. They can also build up moisture and cause problems.

were the issues present both before and after changing the plugs, wires, cap and rotor?

I considered this knowing that the coil's specs were slightly off. That's why I already have a coil on order coming tomorrow. What I couldn't figure out is how the coil is discriminating on Cyl #1. And I could see spark at the end of the wire so I know the coil is firing for cyl#1. And I know the engine runs fine at 1500 and above. BUT you got me thinking.

1. Even though it sparks in free air, it is harder to spark under compression
2. Cyl #1 is the furthest away from the distributor hence the highest resistance plug wire
3. Does the spark get stronger as engine speed increases? Why is it ok at 1500 and up?

So if all these things do happen, and the coil is damaged just enough that it can't spark through the longest wire's resistance and plug under compression under 1500RPM, then maybe it is the coil. Will you all cross your fingers along with me?

Well, coil should be in tomorrow. I'll try it and see. I'm not going to get my hopes up though. I'm just that pessimistic i guess.. I hate having to work on this engine because my plans are to swap it for a 4AGE, but I don't think I'll get that done before I have to have it smogged again. It's something else I'm considering.

[90 GP]

Check all vac lines and rubber grommets where fuel injectors mount into intake for leaks. Check fuel pump pressure and the pressure regulator. Try switching out oxy sensor in spite of it being checked. It could be slow to react if original.

[Tech1984]

If the ECM spit out 25 and 26, that would be a good start. That's showing a very lazy 02 sensor.

[SuperRA]

Originally Posted by 90 GP

Check all vac lines and rubber grommets where fuel injectors mount into intake for leaks. Check fuel pump pressure and the pressure regulator. Try switching out oxy sensor in spite of it being checked. It could be slow to react if original.

The carb spray test included the injector seals near the intake. I can check the pressure once I get a gage with t fittings etc. I wish all cars had a gage port on the fuel rail. =\ The O2 sensor has been changed within the last 5 years or so but yea, that doesn't rule it out.

Originally Posted by Tech1984

If the ECM spit out 25 and 26, that would be a good start. That's showing a very lazy 02 sensor.

Yea I started there and checked everything the FSM suggested to check following the FSMs procedures.

I'll eventually try getting a new O2 when other "free" options run out. At least that part is cheap enough. I really don't want to spend much more on this engine.

[90 GP]

I was assuming the oxy was the original. Seems like you have covered alot of bases already. Be curious to know the culprit when you find it.

[Donald]

A compression testor costs less than $20.
A leak-down check would be good, but a compression test is an invaluable troubleshooting procerure.
A compression check should be the next thing after verifying fuel and spark, otherwize you could be chasing your tail for a long and frustrating time.

Just my 2 cents worth.

[SuperRA]

Originally Posted by Donald

A compression testor costs less than $20.
A leak-down check would be good, but a compression test is an invaluable troubleshooting procerure.
A compression check should be the next thing after verifying fuel and spark, otherwize you could be chasing your tail for a long and frustrating time.

Just my 2 cents worth.

Yep, I checked compression and all the cylinders came to ~180psi.

Originally Posted by 90 GP

A long shot could be a slight coolant leak into cylinder.

You know, I was looking at the exhaust this morning and there seemed to be a white vapor coming out the tail pipe even after warmed up. Aww man I really hope it isn't that..

[blb]

Originally Posted by SuperRA

You know, I was looking at the exhaust this morning and there seemed to be a white vapor coming out the tail pipe even after warmed up. Aww man I really hope it isn't that..

Pull the plugs. If the spark plug from the cylinder that is misfiring is cleaner than the rest, that is confirmation that the headgasket is breached between a coolant passage and the cylinder. I hate to be the bearer of bad news, but the symptoms you describe (misfire at low RPM and not at higher RPMs) is consistent with coolant leaking into the cylinder. This is because at higher RPMs there is more gas in proportion to coolant and it fires, unlike at lower RPMs where there is less gas in proportion to coolant where it misfires.

[SuperRA]

Originally Posted by blb

Pull the plugs. If the spark plug from the cylinder that is misfiring is cleaner than the rest, that is confirmation that the headgasket is breached between a coolant passage and the cylinder. I hate to be the bearer of bad news, but the symptoms you describe (misfire at low RPM and not at higher RPMs) is consistent with coolant leaking into the cylinder. This is because at higher RPMs there is more gas in proportion to coolant and it fires, unlike at lower RPMs where there is less gas in proportion to coolant where it misfires.

Plugs are new so I'll wait a little while for them to get dirty.

I tried the new coil today with no improvement of engine idle. I'm tending to agree with you that it might be this. However, the coolant level is still full to the brim. I did fill it last saturday so i'll let it be used normally for a little while.