Very high idle on start-up and severe misfire when car is hot

[sebas-1024]

Hi, back with more issues

About a week ago I installed my alternator back in the car as I had it fixed, it seemed to work fine for a few minutes but when it got to operating temperature it had a severe misfire and would not accelerate unless I pumped the pedal a bunch of times repeatedly pretty fast, seemed like a fuel pump issue so I had it replaced but the issue persists. I also have a very high idle on start-up, it goes to about 3000 RPMs for a few seconds and then it goes down to about 900 RPMs, wich is roughly where my idle is at. The engine responds well enough before it gets to operating temperature, but once it does it starts misfiring again.

I disconnected each injector with the car running to check if all cylinders were working, and they are.
Also checked for spark in all cylinders, there is spark from the coils to the spark plugs.
Didn't find any big cracks in hoses that could cause such a vaccum leak, but I'm not an expert on finding those so could be missing something.

Any ideas on how to diagnose this correctly? I'm thinking it's a vaccum leak but could use some advice on that

Thanks in advance for any help!

 

[dwb]

Boost leak test. Check for diagnostic codes.

 

[sebas-1024]

Boost leak test. Check for diagnostic codes.

Boost leak test is for turbos, right? Mine is naturally aspirated so it doesn't have that. There is no CEL so no codes either.

 

[dwb]

Yes, sorry, I saw GSX and thought turbo eclipse.

If it happens only when hot, electrical components like the ISC, PTU, broken wires, etc. come to mind. Have you inspected the ECU for leaky capacitors?

 

[sebas-1024]

Yes, sorry, I saw GSX and thought turbo eclipse.

If it happens only when hot, electrical components like the ISC, PTU, broken wires, etc. come to mind. Have you inspected the ECU for leaky capacitors?

Haven't checked those, might as well make sure that the ECU is in good condition. Thanks!

 

[MitsuTimes]

This sounds like a grounding issue to me. Check/clean all of your ground points. Maybe add another if you have the resources.

 

[sebas-1024]

This sounds like a grounding issue to me. Check/clean all of your ground points. Maybe add another if you have the resources.

Just a thought, this same issue happened once before after messing with my alternator, but it went away so I ignored it. Is there anything near the alternator that I might have disconnected or damaged that would cause this? Maybe a ground as you say

 

[MitsuTimes]

Not a ground in that area. There is one on the trans to the passenger side frame rail and one on the intake manifold but the wiring is going on 30+ years old so you never know. The o2 sensor plug is in that area and could cause some similar symptoms so give that a check also.

 

[sebas-1024]

In case anyone is wondering, it seems my issue was simply caused by malfunctioning injectors, they were tested outside of the car and some of them were not injecting enough fuel. Maybe the internal coil was acting up due to being 30+ years old and also getting hot. Got 4 "new" injectors and the car seems to be running well enough for now.