Linson

the car is an '89 Formula 350. it has been mildly, yet extensively modded. the car has under 35k original miles and just about 5k on the motor, and even less miles on some of the other peripheral parts. after port matching the upper plenum to the AS&M LTRs last month, the car had been running better than ever. then suddenly, it would start up and run normally from a cold strart (sitting over night) but then from a warm start (say from a grocery store parking lot) it would exhibit a very high idle (too high to put into gear) or... an erratic idle, and/or once the idle had settled, the car would die when i put it into gear. once i'd get on the road, it would run and drive great. these symptoms have gotten worse and worse to the point that now the car has become completely undriveable.

SYMPTOMS:
upon start up, these cars are supposed to jump to about 1500 RPMs and settle to the desired idle. my car no longer does this and will die unless i give it throttle.

after a couple minutes warm up, the car will hold a slightly rough idle (while seeming to run very rich), but when i put the car into gear, it dies...or drops to 400 RPMs, then surges up and settles to a slightly low idle, or does the aforementioned and drops RPMs again and dies.

i CAN make the car hold idle by adjusting the throttle plate stop screw (something to this effect had to be done so i could drive the car home from the shop), but it must be adjusted to the point that the idle is too high, and the car still runs rich.

WHAT I HAVE TRIED:
i first tried to sort it out myself. then i had my buddy bring his scanner. and finally i took it to the shop. all to no avail.

i replaced the IAC (which was already like new because i replaced it a year ago.) no effect.

my buddy brought his scanner - the IAC and the O2 Sensor read "inconsistent." no vacuum leaks were detected.

took it to the shop, their scanner showed the IAC and O2 Sensor working properly. also the TPS was working properly and fuel supply didnt seem to be an issue. smoke machine showed a fairly significant vacuum leak at the DS bottom front TPI runner (which the car evidently ran fine with for month unless it somehow occured suddenly. no answers there.

today i addressed the vacuum leak by loosening and re-tightening the bolts at the front/bottom runners, tried some adjustments to the throttle plate stop screw, and replaced the custom prom chip with a fresh copy of the same chip - all to no effect.

at this point, i am thinking that the issue is something mechanical rather than electronic (at least i'm leaning that way) but i am stumped, and most mechanics are unfamiliar with TPI so, i am hoping that someone here will have had a similar experience or have some expertise that might let have me concentrate my efforts in another direction.

thanks.

NowhereFast

Based on the gradual progression of it running worse and worse, and the car running rich, I'd have to guess the diaphragm in the fpr may have gone bad. Look for fuel in the vacuum line from the plenum to the regulator.

Linson

Thats beautiful if you're right because I've been wanting to get an AFPR. Could be just the excuse I need. Gonna check out that vacuum line now.

Linson

did not find fuel in the vacuum line. slight smell of gas, but no liquid fuel, even after running it for a minute or so. deal breaker?

Linson

well, i went ahead and removed the upper plenum in order to inspect FPR, but it has the "tamper resistant Torx screws, so im gonna have to buy a tool for that - looks to be about a T-15.

also, the gaskets tore as they got stuck to the plenum somehow (they were adhered to the runners only.) so now i have to buy new AS&M gaskets...again.

NowhereFast

I looked round a bit, and while dripping fuel from the fpr is the most common sign of failure, it shouldn't smell either.

I hope that's your issue, wouldn't want you to have ripped apart your intake for no reason. Gives you a chance to put in an adjustable fpr though. I've heard putting some Pam non-stick spray on the gaskets keeps them from sticking when you take things apart.

maks10

The surging idle thinks vacuum leak but you said it was fixed at the plenum....probably a long shot but check your timing if you haven't already

I would check ur fuel pressure before u buy a new regulator and see if it holds pressure while running and after you shut off engine

TTOP350

iTrader: (8)

Not sure what injectors you have but I would (along with what has been said above) also ohm check those, test the coil, ign module, coolant sensor, maf and pickup coil.
Has the TPS been moved ?

Linson

MAF reads ok. TPS was reading around 0.5 volts, where its supposed to be. the injectors are Accel 24lb/hr.

TEDSgrad

iTrader: (4)

You plugged EGR and eliminated emissions - did you re-flash for that?

Caveman305

iTrader: (8)

i would also question the fuel pressure before buying a fpr, what is your reading

the symptoms scream fuel related issue to me, i was able to keep my TBI running by adjusting the idle set screw when the hose in the tank developed a split, it would eventually idle pretty smooth, but as soon as you drop it into gear it bogs down and wants to die or does

the pump itself was still in working condition, but the split in the hose wouldn't allow enough fuel pressure to reach the motor to keep it running with any load

Linson

sorry for being unavailable for the last couple days. at this point, I'm replacing the FPR with a Holley AFPR because I have nothing to lose by doing so (other than about $100, but its something I've been wanting to do anyway.

removing the existing FPR has been a bit of a hassle...
first, I needed to buy some security torx bits, and the only ones readily available are junk. the first set, the T-10 bit broke off on the second screw. the second set, the holes were not even centered in the bits, although I was able to get all but two screws of with this. for the last two screws, I used the combination of a hammer and a standard torx bit for one, and a set of vice grips for the last one, which eventually broke the head off, but at least I was able to get the damn cap off. fortunately, I have an extra FPR from an '86, the same donor equipment that I used to port match the plenum - so I have an extra lower housing should removing the rest of the screw prove problematic. the diaphragm appeared generally intact, though it seemed a bit dry-rotted and roughed up around the edges. not sure if that was from all the friction/moving that occurred while trying to remove that last screw.

somehow, the upper TPI runner gaskets tore when I removed the plenum. they were only adhered to the runners, yet they somehow tore from the plenum side...so I have ordered to more sets of runners from AS&M to the tune of some 60 or 70 dollars. I ordered the AFPR and a FP Guage from Summit on Monday. since I'm back at work and not on vacation, I'm having very little time to devote to working on the car.

I got a Husky brand security torx bit set from Home Depot which appears to be of descent quality.

Linson

also, the Fuel Pump is a Walbro 255 that has probably less than 2000 miles on it. all other seemingly related equipment (sensors, etc. is like new and is no more than two years old and has seen probably a thousand miles or so...not saying that it cant be faulty, just saying that it is like new.

Linson

of course. it has a custom chip and it has ran well for the last few years. it has always had a bit of hesitation from a stop. I am hoping that upping the fuel pressure might fix that maybe.

TTOP350

iTrader: (8)

You need a local tune if you haven't done that, mail order tunes are shakey for the most part.
I use pam on the gaskets so they can be reused a few times. I have 1 set that has been on 12 different sets of runners.
Have you checked the fuel PSI while running?
Do you have a known good MAF to swap in?

Linson

car has had a local/live data tune. Ed's mail order chip (Fastchip) was really close, as in no real difference at all. i had to replace the FPR base with the one from the '86 donor parts - it was in better shape and i couldnt get the remove the screw that had the head break off. upon a second inspection, the diaphram did seem a bit worn through in places. also, there was some sort of rusty looking debris in there. i have the Holley AFPR installed and am waiting for the gaskets to arrive. i will try that Pam (the spray on butter substitute, right?) trick.

i dont think the fuel pressure was tested, but now i have the new regulator and the guage so i will do it when i get the car put back together. fingers crossed that the FPR was the issue.

Linson

i've got the gaskets affixed to the runners. i doubling up on the gaskets this time. i am on my way to Walmart to buy some Pam.

as far as best practices for torquing down the runners, should i:

a) torque down the bottom first (inner to outer, of course) and then torque down the top? or...
b) bolt the plenum into place and then torque both top and bottom together from inner to outer? and...
does it matter if i do one side at a time, or should i bolt everything in at once (example: inner bottom driver side, then inner bottom passenger side; then inner top driver side, then inner top passenger side, etc.

paulo57509

This is the way I do it.

1. Position the runners onto the lower manifoldand start the bolts but keep them loose. Give the runners wiggle room.
2. Plug in the Manifold Air Temperature sensor.
3. Position the plenum onto the runners and start the bolts but keep them loose.
4. Snug the runner bolts at the lower manifold. Doesn't matter which side you start with. Work inside out.
5. Snug the runner bolts at the plenum. Doesn't matter which side you start with. Work inside out.
6. Go around from bottom to the top/inside out in stages approaching final torque.
7. Done.

Double check that you have the correct gaskets in the correct positions before starting.

Why are installing double gaskets?

Brianbajnuth

Was the fpr the problem?
Got somewhat of the same problem

Linson

nope. I am back at square 1. I shot a couple of videos of the case in point but am having trouble getting them uploaded.

I set up an appointment (10 days out) to take it to another mechanic. he's a little more familiar with TPI than the first guy I took it to, but he's also more expensive.

the car will idle nicely in park if you give it throttle long enough, but then, if you try to put it in gear, she dies - or if you rev the motor, she dies.

Brianbajnuth

I have a very similar problem.
My car will idle really rough at about 700 rpm and when warmed up it will idle at 1300 rpm and still be a little rough but when I put my foot down the back tires break loose. I don't feel a loss of power. I think it's something to do with the idle aire control valve because I screwed it out will the car was running and nothing happened, car didn't stall didn't do anything soo I gotta look into the now

Linson

i will definitely let you know what the findings are once i get this resolved.

Linson

Question about testing fuel injector resistance with an OHMs Meter:

can this be done with the injectors fully installed? or do i have to remove them from their housings and from the fuel rail?

Bob88GTA

iTrader: (2)

You can do it while installed, just unplug and measure away!

Linson

Done. Readings were all right around 14.1 cold and between 15.1 and 15.4 hot.

norcalz28

iTrader: (13)

interested to see what you find out here. I chased some issues with mine last year. It was running rough, and wouldn't go into closed loop. Would die at stop lights, etc. A new o2 sensor took care of all those issues, and the car had been running fine, up until recently. Has developed a bit of a creeping idle when it's warmed up. Did you set minimum air with the esc connector disconnected? Also, try dialing in the TPS again. And cleaning the IAC, if you haven't already.

Will

8Mike9

Really seems like the IAC isn't doing it's job. But the "smells rich" is a bit baffling...

What is your Fuel Pressure, and how long does it hold?

Have you reset min air/idle yet?

I'd have your buddy bring his scan tool back over...in the morning, I'll plug mine in and get proper start up counts for the IAC (disregard O2 at start up/idle)...but as I recall was always around 120 or so?...then as car warmed up and idle went down, seemed to settle around 25-35, or there abouts, been awhile, but will give me a reason to plug back into the car

yaj15

iTrader: (3)

I'm very interested in this thread as I've got a very similar problem on my car. I've also replaced/checked most of the gaskets, vacuum lines, ignition system components etc. I'm going to look in to the fuel system next on my car in a similar fashion to what you are starting to work on.

Linson

I agree that it seems like the IAC is not functioning. it is brand a brand new piece. the one it replaced was like new as well.

reset minimum air idle? not sure what you mean actually.

fuel pressure is set at 47 PSI (per Holley recommendations for AFPR.) further tuning has not been feasible, because the car doesn't run. the fuel pressure holds at 47 PSI while the car is idling (it takes seven-and-a-half minutes of feathering the throttle to get the car to idle.)

as I recall, the O2 and IAC readings were kind of all over the place when my buddy was running his scanner. then, the first mechanic I took it to said that the O2 and the IAC were fine. the car is at the shop now - hopefully i'll here something by Monday or Tuesday.

8Mike9

There's a Tech Article "How to" to reset minimum air and idle.

Must remember that just because the IAC is going crazy, doesn't mean it's bad...IAC controls idle off of a few things...off the top of my head, CTS reading, MAT reading?, something else (besides RPMs)...getting old..lol

Got late and listened to the Giants/Dodger game...effing Dodgers and Kershaw...anyway will be working on my car tomorrow, give you some proper initial scan and run reads.

Like I say...O2 always goes up/down at idle...really only useful info while at speed, when ECM is correcting fuel mixture, at idle, you can be dropping in and out of closed loop, due to exhaust temp not activating the stock O2...IIRC, exhaust temps need to be like 600-800 degrees for the O2 to function properly.

Linson

thanks, Mike, for the technical advice. the O2 sensor is a Casper 4-wire conversion. if the IAC were the problem, would that be evident by scanner readings?

it is day two at mechanic # 2 and they are perplexed. all scanner readings appear to indicate that systems are functioning as they should. tomorrow, they will investigate some mechanical possibilities. first, they'll do a smoke test, I'm sure.

8Mike9

So heated O2..okay, just have to verify what the O2 readings are in closed loop..they will bounce around..no doubt...I don't think that would be an issue so much, if memory serve, the ECM is going to try and keep it around 450mv at idle, check the O2 crosscounts (search this forum for what good numbers are, I forget)

The Scanner will only read what the IAC is doing, the tech will have to look at the rest of the IAC is looking for, to see if it's functioning properly.

I never had to work on an IAC issue, so never delved too deep into the whole control of it.

TEDSgrad

iTrader: (4)

While running, use finger tip pressure on the men cal chip into the ecm. I've seen old ecm's have circuit board issues.

maks10

Hate to see you dumping money and no results....maybe rewind to when ur car was running well....what happened since then? Noticed u changed ur plunum gasket was the base manifold taken off??? If so Maybe distributor wasn't put back in place so timing maybe off? You said u think you were running rich did u check ur plugs to verify that? Also read that ur fuel pressure was set at 47psi...should be 43 psi for our cars stock unless ur chip says otherwise....hope that helps some

Linson

sorry it took so long to update, but I just finally got the car back from the shop where it had been since September 10th.

so, the car IS FIXED. it starts and runs as it should. it is hard to say exactly what the issue was, but whats most important is that the car is running again. according to the Rich, the owner/operator of the shop the fuel trims were out of range (long term @ 105). every other individual system seemed to be working in its own right, however, in relation to each other, the IAC and TPS were outta whack, or at least it would seem. he also reset the base idle and the ignition timing. aaand he lowered the fuel pressure to 37 PSI (to combat a rich fuel condition). I may bump that back up once I put some more miles on the car - she was running really rich for a while, so I want to give it some burn time before I mess with the fuel.

the guy had my car at his shop for a month and a half. but he only charged me two hours of labor, so all told, the car appears to be fixed, and it cost me less than $200. the best part is that Rich was able to eliminate the off-idle stumble which had been an issue since I first got the car on the road back in 2011.

he said that the long term fuel trim was still dropping, but he hadn't road tested it - so it may have just needed to re-learn its fuel/idle/running parameters. I will take it back when the weather clears (in a few months) and recheck the fuel trim. car is running great, but we are now in November where it rains quite a bit here in western Washington until around July, so I probably wont be doing much with it until then.

Linson

thanks again, everyone, for your input on this. it was all solid technical advice. even though its fixed, its still a little baffling (to me anyway).

im just super glad its fixed. out of my three "running" cars, its my favorite.

and, the off-idle stumble is fixed so, again, kudos to Rich at Sequim Valley Auto.

karl's-92'-z28

iTrader: (5)

I would put a fuel pressure gauge to monitor fuel pressure....that's what I'm going do when I put in a AFPR.