Sudden stalling problem

[poetica_payge1624]

Okay, so I was out for a drive yesterday (picked up my boyfriend from work about 11 miles from where I live) and stopped for some food. My '90 Bonneville LE was running like a dream until that point. We were inside for about five min or so and when I tried to start it so we could leave, it was idling at or below 1000 rpm and stalled when I put it in gear and tried to back out of the parking space. Earlier in the day I had topped off the power steering fluid and when it stalled, I topped off the trans fluid and put a quart of oil in. Problem continued. I let it turn over and idle for about 10-15 minutes and was able to get it home... Barely. I cleaned the air filter last night and the carburetor this afternoon, as well as putting injector cleaner in my tank. As soon as it warms up (i.e. idles for 20 min) I can drive it almost normally, but the idle never goes above 1000 and it normally sits at 1500. Any suggestions as to what might be wrong with it?

[SuperHbody]

First of all, this car is fuel injected. Second, what part of the intake did you clean that you thought was the carburetor? Third, you idle shouldn't ever be that high when fully warm which leads me to believe either your IAC (Idle Air Control Valve) or TPS (Throttle Position Sensor) is way off. Did your Service Engine Soon light come on?

[clm2112]

(Just FYI for the rest of the group, the car in question used to be my '90 Bonnie, who's history is pretty well documented here on the forum.)

The problem as described to me over the phone is an erratic idle and poor driveability under any kind of load, the load from the transmission when putting it in gear was enough to stall it out. Engine revs freely with in park with no load on it. As she said, the problem just cropped up after a hot restart.

My thoughts wander towards a vac leak of some sort, but that is just a guess being 900 miles away from the car.

Idle on the car with no load has always been high, I think more like 1200, not 1500, and dropped to about 7-800 rpm when in gear.

As suggested, did you check and of the black plastic vac lines last night. Also, as the previous poster asked, is it throwing any codes? (or at least a constant check engine light.) It should have at least one, from disconnecting & reconnecting the TPS sensor while you were trying to get it started again and home.

(and the "carb" is the throttle body kiddo on these engines. You may wish to search the forum for instructions on how to clean the Throttle Body and Mass Airflow Sensor..aka the MAF...which probably hasn't been done in a while. )

[poetica_payge1624]

It throws no codes. The only time the check engine light comes on is with the other two status lights like I just put the key in the ignition but haven't turned it over yet. Another guess in the household is that the idle just needs to be adjusted. (Not my opinion, and I really don't want to mess with that until I get a more solid answer)

[RJolly87]

I would also want to check fuel pressure, to possibly identify fuel delivery issues

[clm2112]

Another guess in the household is that the idle just needs to be adjusted. (Not my opinion, and I really don't want to mess with that until I get a more solid answer)

Not a good idea. Idle adjustment isn't needed, the TB is set at the factory and there's nothing about the engine's configuration has changed to require a change to base airflow. It's not like a carb where you mess with the idle stop & mixture screws, FI motors only need the screw set for the basic airflow needs of the engine. In fact, if you mess with it, the engine computer will try to undo what you did. The engine is already trying to control the idle now, and mostly succeeding. (Yeah, tried that many years ago on the F-Bodies before coming to understand that the idle stop screw is a misnomer...the computer controls the idle, not the screw.)

No codes is good, tells me the software trying to run the motor still thinks everything is hooked up.

I'm still leaning to a vac leak letting air into the engine. A vac leak allows air into the engine that the computer doesn't know about. Most times you end up with a engine that is running too lean (not enough fuel for the air coming in.) In that situation, the motor can keep spinning, more or less, but falls flat on it's face when you try to accelerate. Same thing that happens when you run it out of gas, fuel pressure drops because there isn't enough fuel, causing a lean condition that kills the engine.

Like RJolly suggested, you can also confirm the fuel pressure is in good shape. You already have a working fuel pressure gauge on the dash. Should be over 40 and under 50, and to my recollection, it pretty much stays in one place all the time, even though there is a vac operated fuel pressure regulator that modulates it by a few psi based on engine load. The gauge powers up as soon as the key is in run, the pressure it is reading is up at the inlet to the fuel injector rail, where the sender is plumbed into the fuel line near the TB.

Also, in your computer stuff (like on the ReadyNAS) you should have two service manuals for the Bonnie, one being the official 1990 Pontiac Bonnie FSM, the other being a Hayes manual for H-Bodies in general. Time to get familiar with them. It's a bit daunting, I know, but reading the overviews of the Emissions and Engine sections would be a good idea now. You don't have to rebuild it, but you should understand the components (what they are called and where they are physically on the car.)

Like the spark plug & wire issue from a few months ago, you are gonna do a face-palm when you figure out what is really wrong with the motor. I'm betting it one or two simple things that are going to be easy to fix.

[poetica_payge1624]

Like the spark plug & wire issue from a few months ago, you are gonna do a face-palm when you figure out what is really wrong with the motor. I'm betting it one or two simple things that are going to be easy to fix.

It probably will be something simple. And I will, most likely, facepalm. I'll take a gander at the manuals to see if I can figure it out. If not, Austin's uncle is trained as a mechanic and is willing to help out. I just feel so.... ... right now.

[clm2112]

Ok, post what you find when you check something out. If you confirm the fuel pressure, or find a broken vac line, etc. note your observations in this thread. So anyone following along and offering advice can mentally cross it off the list of possible causes and maybe see a clearer picture of what is wrong.

Most of the folks on this list work off what they know about the way the car was built and what systems connect to which parts. An observable reading points to several possible problems that can be whittled down by elimination.

For example: You go out and look at the fuel pressure gauge in the dash and it only reads 22psi and it is bouncing around. Everyone knows that is way too low so the engine isn't getting the proper fuel (car's computer can't read fuel pressure so it assumes it to be normal all the time. The gauge is something I added to the car and it isn't hooked up to the computer.) That points a problem in one of the following parts: FP, pickup, fuel lines, regulator, filter, FP Relay, Qty of fuel. Then we start working on narrowing down that list. Divide and Conquer approach to problem solving.

See, as of your last post, everyone now knows that you have access to some extent to tools and possibly a person who can show you how to use them first-hand instead of trying to explain their use.

Another example, that is possibly relevant to the problem at hand, is the HVAC system.. it uses engine vac to operate the shutters that direct air inside the dashboard. If you can't change where the air is blowing out in the dash, that means the HVAC controls are also not getting any engine vac, which points to a really big leak allowing air into the engine. So, if you go out to the car and start it up, then move the HVAC controls, and works, then that proves that the engine making some vac and the check valve that divides the vac system in the body of the car from the engine is doing what it is supposed to do. (Btw, you can also hear the shutters in the dash operate...that little "rattle -clunk" is the sound of the vac servos on the shutters moving in response to the controls.)

[poetica_payge1624]

Okay, I can change where the air comes out of the dash. I hear the "rattle-clunk" noise and it will change from vent to defrost and back. I took it out for a drive again today and noticed when I accelerated, the vac gauge you put on the dash dropped to around zero and when it was essentially coasting, it was sitting at 20. I don't often pay attention to that gauge so I'm not sure if it's normal to be sitting at that number. The extreme fluctuation doesn't seem normal.

[clm2112]

What you are seeing is correct (to be honest, I forgot the dash had a vac gauge, I remember the Fuel Pressure and O2 sensor gauges).

Vac always runs opposite of throttle.

When the car is decelerating, the throttle is closed and the engine is acting like a big air compressor spinning back down to idle, so that's when you typically see the highest engine vac. (Like getting a sock stuck in the nozzle of a vacuum cleaner.) 20 is a pretty good number. Sitting at idle in the driveway should be about 10 to 15.

When you step on the gas, you open up the throttle and the vac drops to zero (you uncorked the motor to draw as much air as it can suck in, so it isn't developing any vac at all...only a little bit caused by the shape of the air intakes and the restriction of the air filter.)

How did the Fuel Pressure look?

[poetica_payge1624]

When I looked at the fuel pressure gauge last, it read at about 40. I'm not sure if that's a good or a bad thing.

[clm2112]

Ok, so long as it stays constant around 40, you are in good shape there. It has always hovered around one reading during all driving conditions (except when I was feeding Nitrous Oxide to the motor, when the extra fuel being dumped out of the rail caused the needle to drop a little.) Otherwise, you normally can't see the little fluctuations caused be the fuel regulator doing it's thing.

So far, looks like the vac system is still OK, fuel system is doing it's thing. That brings us to sensors and the engine controls.
Your first care package should help in that department, but it might be a few days before it gets there. Meanwhile, I would strongly suggest cleaning the MAF and the throttle body. On the off-chance the car does have a stuck or plugged up Idle Air Controller (IAC) cleaning out the inside of the TB might help it out.

To do this, you need a can of aerosol carb cleaner (the kind that is safe for Fuel Injection systems.) and a flat blade screwdriver. You should also be wearing glasses and safety glasses while doing this. Occasionally the engine will choke on the carb cleaner and barf some out. Kinda sucks to get it in your eyes (burns like hell on the eyeballs.)

Take the hose clamp off the TB and remove the ductwork between the air filter and the throttle body. Pay attention to the electrical sensor that is installed in the ductwork. That's the Intake Air Temp Sensor (IAT) and as the name implies, it tells the computer how hot the air going into the motor is..so it can compute the actual density of the air being sucked in and look up the appropriate amount of fuel to add. If you can move the ductwork aside while doing this and leave the sensor connected, great.

Watch out for the big pipe below the throttle body. That's the exhaust cross-over (takes the exhaust from the front cylinder bank and feeds it into the rear cylinder exhaust manifold on it's way to the Catalytic converter and out the back end of the car. That pipe has a heat shield on it, but still gets pretty hot. Don't get your hands, tools, clothes, or wires near it.

With The Engine OFF!

Looking into the round mouth of the TB, you'll see it has a big section with the throttle plate visible. If I recall correctly, I removed the wire mesh screen on the front of the TB years ago, so you'll be able to squirt carb cleaner right into the mouth of the TB. You'll also see a smaller opening on one side that leads to the Mass Airflow Sensor (afore mentioned MAF) The large plastic rectangle on the top of the TB is the actual MAF electronics, but the sensor probe sticks down into that smaller passage inside the TB. Hose that passage down too.

There is another passage on the other side of the TB, that is for the Idle Air Controller (IAC). It is another black plastic can sticking out the other side of the TB. It has a 4 pin connector in a square pattern. We are going to hose out that passage with carb cleaner too to try and clean off any soot built up on the valve and spring the IAC operates.

Ok, once all that is hosed down with carb cleaner. You can hold open the throttle by hand and hose down the area where the throttle plate closes. Since you are not having any problems with the throttle sticking, this area should already be fine, but hey, we are already here.

Important: DO NOT LET ANYTHING FALL INTO THE ENGINE! Not the little plastic pipe from the carb cleaner, or anything else. (BTW, That's what the missing wire mesh screen was suppose to do..prevent anything solid from getting sucked into the engine.) That area behind the throttle plate is the Intake Manifold Plenum.. everything in here leads right to the intake valves on the cylinders and I can assure you they will not like having anything going in except fuel and air. If anything does get in there by accident, stop and we can discuss how to get it back out before starting the engine again.

Once everything has been hosed down. Wait about 15-20 minutes to allow most of that cleaner to soak into the soot deposits or evaporate off the inside of the TB and manifold. Now try to start the car (yeah, Try is the operative word, it may take a few tries to get it to light with all that carb cleaner in there.

When it finally starts up and gets to an idle state, use little squirts of carb cleaner into the TB. The engine will bog down a little on every squirt because carb cleaner doesn't burn as well as gasoline. If you squirt in too much, just wait a minute or two and restart the engine. When you have a very clean throttle body (or an empty can of carb cleaner...whichever comes first.) go ahead shut the engine off and hook the ductwork and filter back up. Make sure everything is connected and take it for a spin around the block. See if anything has gotten better or worse.

Normally I would have you disconnect the batter ground cable at this point, but since we are trying to preserve any stored codes until we can get them read out, just hold off on that. If access to a good scan tool doesn't pan out, then we will use the paper-clip and flashing SES light to see what's up.

On that note, I need another cup of coffee, a pack of smokes, and a little time in the horizontal position.

[poetica_payge1624]

ALRIGHT!!!! After a thorough cleaning of the TB and MAF, The RPMs were spiking and dropping like crazy. After Dad's instruction of disconnecting the battery to let the computer reset and try to find a natural idle, it worked! After reconnecting the battery, the car found an idle it could live with and purred happily for five or so minutes, I put it in gear and it stayed above 1000 RPMs, drove it around the block and let it sit at an active idle (in gear but foot on the brake) and it didn't dip below 1000! I apologize for my over-enthusiasm, but I'm just so glad it was a problem that didn't cost me more than $30. Thank you for your suggestions and your help.

[clm2112]

Mischief Managed! Well Done Kiddo

[SSEBonne4evr]

This is a classic ICM connector issue.
Take the screw out pull the connector off,
put it on and off 2 or three times, tighten up on the
sockets with a tiny screwdriver.

[1oldman]

This is a classic ICM connector issue.
Take the screw out pull the connector off,
put it on and off 2 or three times, tighten up on the
sockets with a tiny screwdriver.

Would putting a little di-electric grease to any good too? - BC

[clm2112]

Classic or not, It doesn't appear to be the case this time around. Probably nothing more than a plugged up IAC or filthy MAF sensor.

She's going to be doing front brakes in a few weeks, so we'll see if the acceleration problem returns. The ignition module connector was cleaned and repacked a few years ago while working a cam sensor problem so I'm not too concerned about that connector. She should also have a spare ignition module in the kit of extras, if not I can always raid one off the spare motor in the basement. (Yeah, I still have a rebuilt 3800 in the basement, U-Hauled all the way from Florida.)

As far as packing the connector, I used Quicksilver marine grease, which is similar to the stuff used to pack the relay & harness connectors in (water-resistant and plastic safe). Probably any kind of grease in the contacts is better than just leaving them dry.

[SSEBonne4evr]

Disregard my post.

posted on the wrong page.