350 TBI issues

[ManiacMagoo]

I have a 92 GMC k1500 Suburban with 245k I bought not to long ago and shortly after started having issues running. It has a 350 TBI in it.

Problem 1:

It idles fine out of gear and runs fine driving until you let off the throttle then it falls flat on its face if you abruptly let off the throttle. Dropped tons of brake cleaner on it not finding a vacuum leak. Then it recovers after about 5 seconds and idles fine. Mainly only does it in gear when ever you let off the gas.

Problem 2:

Was a quart low on tranny fluid but it shifted kind of weird since I got it. It holds 1st till around 3-4k before letting it shift to 2nd then almost instantly jumps to 3rd with a hard shift. If you floor it WOT it down shifts revs up past 5k like it is slipping then after about 10 seconds shifts and goes.

For problem 1 here is what I have done already. I replaced the fuel filter and pump, TPS, MAP, EGR seonsor, plugs, cap rotor, rebuilt TB, fuel regulator, and temp sensor. After driving on a 300 mile trip it started throwing code 22 and 32. I replaced EGR sensor and code 32 left and replaced connector on the new tps and 22 left. It feels like the timing advance isnt working so I replaced the timing connector as well to make sure it had a good connection. Always throw code 12 but I was told that is normal. Now if I unplug the vacuum line to the egr sensor or map sensor it stops acting up. I took the HEI module in and had it t4ested and was told it is fine. Seems to mainly do it after it warms up. At this point I'm leaning at a crack in the egr track in the intake, bad HEI module after it waarms up, faulty new tps, or a bad distributor. At this point I hate the thing.

For problem 2 I replaced the fuild and filter nothing smelled burned and no suprises in the pan. So I put 1 bottle of Lucus in and still nothing so now I think this is more of an electrical issue caused by problem 1 or atleast Im hoping it is. I'm going to add a grounding strap to the tranny. The shift points are all over the place now.

So thanks in advance to anyone who might have an idea. Sick of tossing money into problems to not have anything cured.

 

[TreeClimber]

I don't know about these exact combos,
but check and see if you have a vacume line down to the transmission, such as on a TH400. Perhaps you've got a bad vacume modulator, or modulator hose.

 

[Binder]

Code 22 is TPS low so I'm guessing you didn't adjust the new TPS when you installed it? What do you mean by "the codes went away"? Did you clear the codes? If you plug the MAP sensor vacuum line it stops acting up as in drives and runs good??????

 

[crash2]

Code 22 is TPS low so I'm guessing you didn't adjust the new TPS when you installed it? What do you mean by "the codes went away"? Did you clear the codes? If you plug the MAP sensor vacuum line it stops acting up as in drives and runs good??????

Some out of the box are not adjustable(2 mounting bolt holes are not oblong)--you have to physicly bend the arm that rides against the TB....

 

[ManiacMagoo]

Yes I cleared the codes. The low volt code was from a bad connector so it was replaced. it is a 2 screw deal non adjustable. Will look into the bent arm part though. Yes if I create a vacuum leak it runs better just eats gas. It feels slugish driving around partial throttle.

 

[ManiacMagoo]

I don't know about these exact combos,
but check and see if you have a vacume line down to the transmission, such as on a TH400. Perhaps you've got a bad vacume modulator, or modulator hose.

I forgot to mention it has a 4L60E transmission so no vacuum lines.

 

[Binder]

You need to adjust the TPS. I stole this paragraph from the Binder planet FAQs.

3. TPS-throttle position sensor. With the idle set, you need to now set the TPS. This need to be set to about .54V. I normally shoot for about .6V.
The TPS is on the passengers side and will have 2 screws holding it on. The factory TPS will not have much room in the holes for adjustments so I use a drill bit or file to elongate the holes as needed. To adjust, just loosen the screws and trist the TPS. You can monitor the voltage on Pin B of the connector with the key on or at pin C13 of the ECM. You can also see it on the sensors tab of winaldl!! Anything away from .54V will also show as a percent of throttle. Such as .2 percent or 1.7 percent...depending on how far from .54 you are. I try to keep the idle setting to within 1 percent.
This is also a good time to check your TPS. Once it is set, just watch the voltage as you open the throttle. you should see a steady rise in voltage up to about 4.5-5V at WOT-wide open throttle. If it jumps up and down or skips some then you may want to replace it.

You need to quit throwing parts at it and make sure the things you do are correctly done. Your original problem may have not been TBI related at all but now you've changed enough things that you probably have multiple issues and it will be that much harder to figure out.

 

[Binder]

Yes if I create a vacuum leak it runs better just eats gas.

You unplugged the MAP sensor and drove it and it ran better?

 

[ManiacMagoo]

Yes it gets rid of the stumble but it dont matter if it is the map sensor or the vacuum line from the egr sensor to the egr valve. I know dont make sense but it does it. Both sensors are new and the vacuum lines are too. When it stumbles it almost dies with either one of the vacuum lines disconnected and it doesnt matter which one.

 

[Binder]

Does it have a mass air flow sensor also?

 

[ManiacMagoo]

Nope

 

[Binder]

Have you tried to do anything else to it not listed? Try to adjust anything like idle speed or timing?

 

[ManiacMagoo]

I have checked timing multiple times have not touched idle speed as it is right around 600-700 in gear and 800 in park. Could the IAC valve cause this? It's I think about the only sensor I havent replaced yet on it.

 

[Binder]

Could the IAC valve cause this? It's I think about the only sensor I havent replaced yet on it.

Don't try to adjust the idle as it's controlled by the computer. I doubt the IAC could cause all of your problems but it could contribute to them. To check it.....More stolen from Binder planet FAQ.

You need to put a jumper between pins A and B of the connector. These are pins A9(wht/blk) and A12 (blk/wht) on the ECM. This puts the ECM into aldl mode. Turn the key on (not start) and the IAC should drive completely closed. You will normally hear a buzzing from the IAC.............. Now unplug the IAC connector. turn the key off. Remove jumper. Start motor. If the idle is too low you may have to keep it running.

After this check if there is air being sucked in through the hole directly above the IAC and under the air cleaner. The IAC should be closed so there should be no air. After this turn off the engine and plug the IAC back in and start the engine. Now there should be air sucked into the hole...
That's about as good as you can test it without more test equipment as far as I know..

 

[zukkev]

Problem 1-->does it still stumble when letting off the gas? If so, most likely cause is the EGR valve itself is opening too far, and not closing quick enough when coming down to idle--seen it 100's of times! Best to replace with a Delco unit, as they don't use the orifice washer like the aftermarket ones, but they will work if the correct orifice washer is used:awesomework:...

 

[crash2]

I have checked timing multiple times have not touched idle speed as it is right around 600-700 in gear and 800 in park. Could the IAC valve cause this? It's I think about the only sensor I havent replaced yet on it.

Kevin had good advise--I have seen where the EGR opens too far or the pressure valve inside has failed and the valve does not regulate properly (neg or pos valve). But yes I have seen where an IAC is worn and reacts slow--too slow to reacts to quick changes.

 

[Bill USN-1]

More stolen from Binder planet FAQ

Thief!!

I would also suggest reading the map sensor input at the ecm and compare the reading with vacuum/map table.
You may want to unplug the ecm connectors and reconnect just to make sure the connections are clean.

 

[ManiacMagoo]

Decided to check the IAC today as to Binder's instructions. Get the jumper in valve closes but theres a small gap between the IAC and gasket hum. I grabbed the IAC and it wasnt even finger tight. I removed it and part of the gasket itself is missing. Im off now to get a gasket and hope that was the weired issue I have been having.

 

[crash2]

Decided to check the IAC today as to Binder's instructions. Get the jumper in valve closes but theres a small gap between the IAC and gasket hum. I grabbed the IAC and it wasnt even finger tight. I removed it and part of the gasket itself is missing. Im off now to get a gasket and hope that was the weired issue I have been having.

One thing you gotta remember--just because it can be ran in/out doesn't mean the IAC is good.

 

[ManiacMagoo]

True and that didn't solve a thing. Well if I leave the Temp Sensor unplugged it runs perfect besides raising its idle about 100 rpms by unplugging it. So I'm wondering it there is an issue with the wire from it to the ecm or if it is an ecm issue.