Same problem new motor..

[TrueChevyTech]

87 tbi 350
Engine idles fine hot or cold, but when warmed up if i ever so slightly push the gas the engine will stumble, although i can accelerate right out of it without hesitation. this was the main reason I spent a load of cash and had it rebuilt.. either way the motor was wore pretty bad so no wasted dollars there.
I get error 33 out of my check engine light which refers to map sensor i've been researching test methods although it seems I don't have a friend with a vacuum pump, any other ideas?
also the oil pressure gauge goes way down to 15 psi at idle.. i'm going to hook up a manual gauge to test it and just use the stock one as a reference .. that sounds like the correct first approach to me.

[79k30dually]

Assuming you reused the original sensors, verify your oil pressure. I'd look at the 5 volt reference and ground circuits on the map and tps. On your data list you can verify your vacuum to the map with a vacuum gauge. Distributor condition? New fuel filter? fuel pressure ok? I could help more with a data list print. I'll try to help, Ron

[TrueChevyTech]

i'm not sure I know what a data list print is, i'll have to get a vacuum pump but even harbor freight is $40 for one, I could just buy a new MAP sensor

[79k30dually]

Data list print is just the information from the scan tool data list. Do you have a scan tool? A basic vacuum gage will do to test the map. Some auto parts stores have a tool loan program. Ron

[TrueChevyTech]

As far as a scan tool, I have a paper clip and barely know how to use it.I dont have even just a standard vacuum gauge. I'll buy some tools but we need to control ourselves, I'm the one that needs controlled I mean.. As far as some more info. most sensors are from old motor, except the ecm water temp sensor and the oil pressure sender for the gauge.

[79k30dually]

How does the brake pedal feel? The code 33 is for high voltage/low vacuum, vacuum leak is a possibility. Carefully spray carb cleaner or penetrating oil arround the base of the throttle body, while the engine is running, listen for a change in the idle. These engine were also known for splitting the elbow on the front of the TB to the pcv valve. Does the idle speed seem high? Let me know and we will go from there. Ron

[TrueChevyTech]

I cleaned the IAC tonight and now it doesn't idle at all guess I broke it, will have to replace it
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[BigDan3131]

Did you have the throttle body rebuilt or did you not touch it?

[TrueChevyTech]

I didn't touch it although it had these symptoms after sitting for a couple months before i pulled the motor

[79k30dually]

Remove the battery cables and hold both cables together for about 2 minutes. This will discharge the capacitors in the ECM, thus reseting the learned memory. Then start the engine, you'll have to give it some throttle to keep it running. Did you take the plunger out of the motor pack after you removed it?

[TrueChevyTech]

Originally Posted by 79k30dually

Remove the battery cables and hold both cables together for about 2 minutes. This will discharge the capacitors in the ECM, thus reseting the learned memory. Then start the engine, you'll have to give it some throttle to keep it running. Did you take the plunger out of the motor pack after you removed it?

Yup that is a big no no, actually i pulled it out of the throttle body and plugged it in and turned the key on and off and on again, it shot out on it's own .. haha I learned but it cost me $30, also i put the new one in and it idle and started slightly better then (random thought) I walked to the EGR and pulled the vacuum line off. my stumbling problem lessened a bit, so i then unplugged the EGR solenoid and it is even better. I'm not so sure this will pin point anything. I had some throttle body cleaner and made an attempt the spray around the TB gasket, the front in particular and didn't notice a change. I will have to do the battery cable trick tomorrow, I'm also very curious of my fuel pressure

[79k30dually]

How did you set the timing, at what?

[TrueChevyTech]

Timing is 0 BTC with the advance wire unplugged
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[rs72z]

The egr could be the problem. But before you start throwing money at it you need to check the fuel pressure. The crappy fuel that we have now will eat up the piece of rubber hose from the fuel pump to the pickup tube and cause a lose in pressure. If that is the case when you drop the tank go ahead and replace the pump or you will be doing it again. I ask me how i know

[TrueChevyTech]

I am going to get a fuel filter , and also would like to know what fitting and what test gauge to use/buy cheap like harbor freight preferred, if I got just the fitting I could just use an anhydrous ammonia gauge from work, it will read down to 0 but not as accurate that low I'm assuming. Also would the fact that I have 5ft of exhaust on one manifold and 6ft with a glass pack on the other matter?
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[TrueChevyTech]

how does this make you feel lol
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[TrueChevyTech]

The fuel pressure gauge worked I got a reading of 12.5 psi although I didn't get a chance of letting it warm up, I used vacuum gauge on egr and it held. Replaced fuel filter and tested throttle body side of egr solenoid and it didn't hold pressure also when stumbling slightly above idle the egr is completely open is this normal? Also engine ran fine for a minute or two after new filter was installed, so confused. Injector pattern looks good idk what's left..... Fuel pressure regulator spring possibly? Read allot of Chevytechs posts on similar symptoms... Btw I am not him and am not jacking his name. I'm truetech on various computer related forums and just threw Chevy in since name was taken . thanks for dealing with my babbling
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[79k30dually]

Fuel pressure should be 9-13, so thats ok. The EGR should not be opening without the truck moving. Disconnect the vacuum line to the EGR solenoid and plug it, Test for the stumble again, it won't hurt any thing to go on a test drive with it disconnected. Sounds like the EGR solenoid is bad. To test it with everything hooked up, connect the vacuum gage to the line at the EGR valve, You should have 0 vacuum at idle and off idle without the truck moving. Ron

[TrueChevyTech]

Yeah slightly above idle the egr opens all the way, does the gear indicator on the column matter? I'll put a vacuum gauge in line from egr and solenoid tonight
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[79k30dually]

The vehicle speed sensor input is a controlling option for the EGR. Ron

[TrueChevyTech]

the speedometer works, it's about 5mph off at 60mph is all

[79k30dually]

disconnect the vacuum to the EGR valve and plug it, then retest. The ECM doesn't open egr valve until the truck is moving.

[TrueChevyTech]

Replaced solenoid for egr and it still stumbles either egr is bad or not enough back pressure from exhaust, next step will be exhaust since it will need it anyways, I'm thinking double glass packs each side I'll be buying the pipe and fittings and also a cheap wire welder to get it all put together, it's the cheapest route I can think of
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[TrueChevyTech]

Got a little update, exhaust is on and sounds great, did test and the egr is opening itself slightly above idle , there isn't vacuum coming from solenoid while parked at all next step will be to attempt to clean the egr, any suggested method?
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[79k30dually]

Carb cleaner and and small brush, Ron