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940 Rough idle, fuel pressure issue?

Swapped out the injectors for another set of green tops, no difference at all. The hesitation is still there. Ugh... this is getting annoying!

Could the neutral safety switch cause any problems? I'm just thinking, since my friend pointed out last week that my reverse lights didn't work. After checking the fuse and probing the reverse light bulbs, I believe the neutral safety switch has failed. IIRC, it provides a signal to the ECU to raise the idle in P and N.

Neutral safety switch prevents the starter from engaging if the position of the switch is not in either Park or Neutral. Afaik your idle will not be affected by a failed switch(had it happen on a 240 and it didn't affect idle).
 
Does anyone know if the IACV is supposed to move freely like other valves I've seen? When I took it out to inspect, it feels like it has a spring to hold it in place. My spare from my 240 (which is pretty gummed up) does the same. Seems pretty odd.
 
Don't think the IACV is the issue... I cleaned out another spare I found since it was in even better shape, and it seems to move easily enough. After driving it, I noticed the hesitation/sluggishness is up until around 3000 RPM. After that, it seems to accelerate normally. I tried shifting it manually from L to see if it's actually starting in a high gear (I knew that wasn't the problem), and that didn't change anything.

I checked the fuel pressure again though, and it looks much better. Primed to 40 PSI (or something like that, don't remember exactly) and idled right around 37 PSI. When I pulled the vacuum line from the regulator, it went to 42 and stayed perfectly steady.

I'll try a running compression test tomorrow and see what happens. I loaded it up on the brakes, and it didn't miss... seemed to run fine.
 
After driving it, I noticed the hesitation/sluggishness is up until around 3000 RPM.
This happened to me once when my spark plug cables failed internally. There was no visible sign they were bad, but replacing them fixed the problem. Did you already try swapping those out?
I hear there's supposed to be some type of heat shield between the exhaust manifold and the spark plugs, but those are long gone on my car.
 
This happened to me once when my spark plug cables failed internally. There was no visible sign they were bad, but replacing them fixed the problem. Did you already try swapping those out?
I hear there's supposed to be some type of heat shield between the exhaust manifold and the spark plugs, but those are long gone on my car.

Interesting. I replaced my wires not too long ago (less than 3k miles), but I guess it's possible that one of them is bad. I got them from FCP, so I could always replace them under warranty.

There are 3 heat shields that attach on the exhaust manifold. All of mine are there. I'm sure it's not too uncommon for them to rust apart and fall off.
 
When I had the problem, it was on a set that was only a few months old. I use Duralast wires. I'm not sure if FCP's have any difference in quality control. It's happened to me more than once, so I have to assume some wires are just duds.
 
When I had the problem, it was on a set that was only a few months old. I use Duralast wires. I'm not sure if FCP's have any difference in quality control. It's happened to me more than once, so I have to assume some wires are just duds.

Huh, that's interesting. I went with the STI wires from FCP. I know Bougicord is the choice for these cars, but I haven't heard anything bad about the STI brand for them.
Hell, for all I know they were DOA and have just been getting even worse.
 
It might be worthwhile to measure the resistance on each wire and see if one is way out of range. I wish I'd tested my failed wires when I had them so I could give you some numbers to look for.
But the symptoms really do sound similar. It bucks and struggles until you get up to speed and then it does fine, right?
 
It doesn’t really buck, but it just feels like it has no power. Then at around 3k RPM, it all of a sudden starts moving. Then of course the horrible idle.
 
Checked the resistance in the wires today, nothing crazy. They were all relatively similar, going down slightly on each wire according to length. Pretty much as I expected. Not really a way to totally rule out bad wires, but reistance wasn't excessive. They were between 4.5K ohms and 9.64K ohms.

From my reading on the LH 2.4 books, I'm down to a few things aside form mechanical.

Radio suppression relay (unlikely since the injectors are getting power)
Fuel system relay (how often to these intermittently fail like this? I figured these usually just die and that's that)
O2 sensor
IACV signal (I'm going to check this tomorrow)

I will try to do a running compression test tomorrow as well, hopefully the rain holds out for me. Its timing wasn't in my favor today, and of course I had something else in the garage.

All else aside, could my cam timing have anything to do with this? The sluggishness started before I installed the cam (along with everything else) but I want to put it out there in case it’s a problem. It’s an iPd turbo cam at stock 0*. I read that it could a little rougher, but unless my engine mounts are just that shot, I don’t think it should idle this bad. And it certainly shouldn’t be so sluggish from a stop.
 
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Yes, the gear is mounted properly and the timing mark is perfectly lined up.

Just did a dynamic compression test. Here are the numbers...
The first is the running compression, the second number is when I blipped the throttle
1- 10-50 PSI/~90 PSI
2- 10-80ish PSI/100 PSI
3- 10-80ish, averaged around 50-60 PSI/110 PSI
4- 45-85 PSI (the check valve appeared to hold this time)/105 PSI
 
Maybe a stupid question... maybe not. The engines shakes like hell. It looks like it's about to jump up and flip around. Like an out of balance washing machine. I know it needs engine mounts, but could those cause the vacuum to flutter like it does?

Aside from that and the down low sluggish-ness (possibly cam timing now that I think about it more) it feels good in the higher end. The gauge flutters a little in boost as well, but when cruising at speed, it stays pretty steady around 20 in-hg. I'd still expect it to be higher (25ish in-hg) though.
 
I understand that the cam gear is lined up, but are you certain about the crank gear too? And for reference, my kid's '93 940T with an Enem V15T (stock beyond that) draws 18-19 in/hg at idle, so you should very much be in that neighborhood. Also, I see you said your valves are adjusted, what clearance did you use?
 
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I understand that the cam gear is lined up, but are you certain about the crank gear too? And for reference, my kid's '93 940T with an Enem V15T (stock beyond that) draws 18-19 in/hg at idle, so you should very much be in that neighborhood. Also, I see you said your valves are adjusted, what clearance did you use?

Yes, crank is perfectly aligned. Cylinder 1 is definitely at TDC with the crank marks aligned. Yeah, my vacuum is definitely way off.

I believe I have them all at 0.015". The cylinder 1 exhaust valve may have been at 0.013" IIRC, but that's still within spec. I know it's not ideal, but I didn't have any shims to correct that. Worst case, it's not hard to order the right one and swap it out. I need to check my notes again to make sure.
 
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