Replace engine light came on, but only once.

[slack]

So your oil pressure was fine and it was just the oil pressure sending unit for idiot light that was bad?

[Pretty much broke]

Yep. Oil pressure is actually surprisingly good on this thing. 30-32 lbs at operating temp. But now Im back to focusing on the running issues. It's getting worse as time goes on. Not as bad as it was last year but it is slowly getting to that point.

[slack]

Oh nice!

For the IAC, is it possible that it's going bad?

Here's the info from fordfuelenjection on how to test it:

This is really easy to test. First as with all problems you should gather the trouble-codes from the computer. Follow the codes for testing and repair. If you get a code that points to a problem with the IAB start the vehicle and bring the engine up to operating temperature. Allow the engine to idle without any driver input to the throttle or pedal. Go under the hood, and disconnect the electrical connector to the IAB. If the engine begins to stubble or stalls the IAB is functional and does not need to be repaired. If the engine idle does not change you should remove the IAB for inspection.

The IAB can pass and still need repair, or it can fail and not need replacing. The plunger and internal spring can get clogged with dirt and oil. This will slow down the air flow and not allow the IAB to function properly. Remove the IAB and clean it. There are 2 halves to the IAB, and you can not buy just one half, but you can take it apart to clean it. But if the internal solenoid is faulty the IAB needs to be replaced.

Link to full article: https://web.archive.org/web/20101201...index.php?p=39

[Pretty much broke]

So instead of me just trying to explain what its doing I took a vid of it running at light load doing it's running rough thing, more info in the video. Heres a link to it, any help is appreciated! Rough running sound clip: https://youtu.be/a3lJQ71Nld4 And thanks for the article slack! I'll check that out tomorrow.

[lincolnlarry]

Once you push down on the pedal a bad IAC should have no effect on the engine. Not sure what's going on with that rough sound though.

[Pretty much broke]

I'm at a loss as well. Essentially the only sensors I haven't replaced are the o2s and the map sensor. O2s are old but the map is fine. I did notice the vacuum to the EGR is very weak. But from what I remember its always been like that. I would drop the exhaust but I've got this small tube that attaches from the y pipe that goes into the engine bay which would make me have to cut it to take the exhaust off. And I suck at welding so I can't really do that.

[Pretty much broke]

So I unplugged both o2 sensors and drove it. Which made a slight improvement but nothing spectacular. The strange thing is, no CEL. With both unplugged it never lit up. Could I have a bad ecm? I tried unplugging the EGR and IAC and same thing. Only thing I've got it to throw a light for is the TPS which throws immediately. Seems strange. Under WOT it pulls hard and has great power. But at light throttle it hesitates and chugs. It also refused to give my friends scanner any codes at all while running. Opinions?

[sly]

these cars are weird that way. Takes a while to throw codes for O2s and usually when it throws a code for an O2, it's actually for something else.

[Hearsesrock427]

The EEC-IV computers rarely fail on these cars.... my money is on vacuum leaks (can have an "invisible" leak that exists despite passing the lit cigar test.... read about them on the Corvette Forum IIRC). Assuming you're still on your original lines, I'd expect at least some of them to be in bad shape. Just based on the age of these cars and all the heat cycles they've been through. SEFI isn't as sensitive to vacuum leaks as CFI, but it can and will run dumb if you have a big enough leak. Won't usually be undrivable, but there will be running issues.

Then there's the fact that vacuum leaks are one of the few things you haven't conclusively ruled out.

[gadget73]

Sounds like an EGR valve hanging open almost. Does it run any different with the EGR unhooked? How about when you force the EGR valve to open with vacuum? It should run no different unhooked, and it should stall or nearly so with it forced open at idle.

The ignition pickups can get bitchy and temperature sensitive. They can also act a lot like a bad TFI.

Is the timing set properly? Does it hold steady? Sometimes a bad pickup can make the timing show up funky.

Have you ever put a voltmeter on the TPS to see what it does? It should read about 1 volt at idle, and smoothly increase to something over 4 volts at wide open. Do this with the key off or you're liable to blow the motor up. You want to measure from ground to the green wire on the connector. Paper clips work nicely as probe tools.

http://www.lincolnsonline.com/tech/00127.html

[Pretty much broke]

Vacuum leaks could be a problem, these are mostly original lines and check valves, and this all started after I pulled the plenum to do the VCGs so maybe I busted something, but I've bathed this engine in brake clean and didn't get as much as a small sputter. Ive tried unplugging the EGR at idle and it ran the same, but never put vacuum to it. And I also just plopped my TPS on, I never knew you had to adjust them, whoops. It runs the same on the old and new dizzy, and it will hold timing just fine on both. It may be a bit retarded at the moment because I set it to 10 degrees but it wasn't fully warmed up. BUT, I pulled codes again and it gave me an 18 this time, which the new dizzy never gave me. And if I remember right it liked 12 degrees better the last time. Hindsight is 20/20. I get flustered and rush these things, always kicks me in the ass afterwards :/ Another thing Im noticing is that it runs bad now regardless of temperature. And it ran the worst today than it has all year. Missing slightly under heavy throttle which it never used to do. And even slightly at idle. Boy, Im beginning to wonder how difficult a SEFI to carby swap might be haha.

[Pretty much broke]

Tested the TPS which was 1.02 at rest and 4.83 at WOT with no dead spots. And unhooked the EGR which made no difference in how it ran. But when I forced suction to it, it did want to die. I did notice that if I blew air into the EGR the diaphragm would seat all the way back, and when I let off it seats just past where you can see it in the holes. Could that be an issue? And also, the vacuum line to the EGR has constant vacuum which I read is bad. Its relatively weak but its there. Is there a way to test the solenoid? And I was going to set timing but the guy witih the light isn't home today and none of the parts stores around here have one. Go figure.

[Pretty much broke]

Well gadget, I think you're onto something. The EGR is very erratic and fussy about when it opens and closes. And at load runs better with the vacuum hose off than on. I didn't drive it but just on the gas on my hill seemed to do it. Could a failing solenoid cause these issues? In park revving and holding the engine it would open about half the time and only for a second before it closed again. Otherwise it would stay shut. I'm also wondering if this could be related to the hiss I hear in the cabin while driving when coasting. On the gas it goes away but coasting it hisses pretty loudly. I sure hope this is the issue, I'm getting real tired of this thing running like dog shit. And it still misses with the hose off, but that feels more like a timing thing rather than EGR or electrical.

[gadget73]

you should not have constant vacuum on that line. Follow it back to the solenoid that controls it and have a look at that. There is a plastic top that will pop off and there is supposed to be a foam filter in there. Its probably dust, so just clear that out and make sure the tube down into the solenoid isn't plugged. Give it a honk of WD40 (or similar, just nothing that will melt plastic) into that tube and into each of the two vacuum ports on it to see if that makes it quit being bitchy. If not, change the EGR solenoid. they do go bad sometimes. I had one get sticky on my car and I changed it. WD40 made it go, but I only actually ran it for about a week until the new part came in the mail. No clue how long it would have lasted, but I suspect the real issue with mine was simply dirt making it hang up.

Pull the EGR valve itself and clean the pintle and the hole it seats into as best you can. if its got nuggets of crap in there, it will stick and hang open. Engines do not like EGR at low speed, and if the control solenoid is sticky it will go full open when it should be just cracking open. Unfortunately that won't set a code either.


You've got it at 10 BTDC with the SPOUT unplugged right? If thats not unplugged, the timing will be very retarded from where it ought to be. If you didn't plug that back in, it will set a code 18. If all that is correct, and its setting a code 18, see if there is any difference in idle when you unplug the SPOUT connector. If no change, either there is a broken wire or that TFI is whacky.

[Pretty much broke]

I sprayed some WD in the solenoid, and wouldn't you know it. It actually helped a lot. It really only does it's thing going up hills now. I'm gonna keep messing with it and see if I can get it working better. Also the timing was about 6 degrees off, was idling very high but it's back to normal now. Spent almost an hour looking for the spout that one of the timing light wires pushed into the dark abyss that is my engine bay. But I eventually found it, right behind the grill. How it got there, I don't have a clue. Also putting my small wheels and tires back on. I like the nose down ass up look but I've lost too much power for it to be worth it. (245 75 16s in the back). With stock gearing and those tires it really doesn't like hills very much.