Chevy & GMC Vans

Been having lots of problems getting my van to idle properly. Went in with meter and checked TPS first this time around because I changed the EGR last round as well as IAC.

These changes helped but overlooked checking TPS at that time. Now I'm getting 5.5-6.2 V when checking grey(+) and Black neg., but when going to Blue + then black again neg. no response or fluctuations.

Assume its NFG, also the electrical connector housing is chipped on the corner leading me to believe time to replace.

Will this cause my high idle? Will change the TPS and start over from start again if its not changed anything after replacement.

Looks like one needs to remove the TB, or is anyone full of tricks today or even tomorrow. LOL

I've had to replace the TPS on mine a couple of times. It is kind of a pita to get to the screws to remove it. If memory serves, the bracket that holds the map sensor and egr solenoid is right in the way of a straight shot into the tps screws.
But, it can be done without removing the throttle body. If the fasteners are torx screws, I suggest a cheap set of small torx bits and a small ratchet.
mine were phillips head machine screws. Fortunately, I happened to have a 90 degree phillips screwdriver that I was able to get the screws out with. I know, it sounds kinda like a left handed metric screwdriver, but it's a real tool I bought many years ago. -has a phillips head driver on one end, and I think what is called a reed's head driver on the other, bent in a 90 degree S or Z shape with a knurled handle in the middle.
If you need a phillips head, another suggestion is a phillips screwdriver bit and a box wrench.
Access is limited, so you have to kind of gum at it a while, but it's faster than removing the throttle body by a long shot.

You have to open the throttle to see the voltage changes. The gray wire is the 5 volt reference, the black is the ground and the dark blue is the return signal to show the computer the value. But than your digital multimeter samples at a very slow rate, to see a glitch you have to have a digital storage oscilloscope.

High idle on a throttle body motor a lot of times is a gasket shriveling up and sucking into the intake, or it could be a vacuum hose some how leaking. Check around the throttle body.

Thanks for the pointers Mike. Now if I'm getting no reading at all with the blue and black I'm assuming the TPS is NFG.???

Am I misunderstanding the procedure to check here, found 5.5-6.3V at the grey and black, am I supposed to move the throttle to get a reading off blue and black even if I don't get .05V without any moving Throttle ?

Also as mentioned the corner being chipped off the connection of the TPS to 3 wire harness.

NO my meter doesn't have oscillioscope features. Is this going to give inadequate readings?

My base gasket appears to be good with no leaks using wd40, no leaks at vacuums sources any longer, fixed these last round.

So being that I purchased a new TPS for $80 and a new base gasket should I decide to remove TB.

Is the Throttle Body a real pain in the arse to R&R, any specialty GM genuine tools needed, other than this tool? LOL !

I am looking at replacing the gasket regardless of no leaks because its only been there for 460,000km., probably a good reason to tackle when this close to the problems, my back and fat ass limits me to repairing this beast inside the bonnet and sometimes takes forever to complete a simple task .

LOL, thanks for your support.

rebuilding the throttle body is no big deal. No special tools needed.( assuming you don't consider a torx driver special). a single edge razor blade comes in handy for removing gasket material. If you have a service manual of any type (Haynes, Chilton) they should have a write up on how to do it. My Haynes manual does.
the rebuild kit is cheap.
One other suggestion along Mike's line of thinking is to check the throttle plate to ensure it is not sticking in a slightly open position.

Thanks for all the pointers there guys.

Done deal with R&R TB, changed Base Gasket, TPS, and IAC. Back to normal idle but getting this sort of pulsating, then flat spot, with fluctuations in my oil pressure gauge now.

My IAC was checked for proper adjustment as per Haynes manual. But just realized I may have overlooked comparing pintles to confirm they are the same type.

Reset pcm with a 20k drive. She's idles like a dream again but need to get to diagnostics again.

Any insight or tips are greatly appreciated.

Update to issues with another question. Engine still pulsates on take only, and will really hesitate , pulsate the gas, and sometimes stall going reverse. Once cruising down the road shes a purring.

My IAC appears to be toast, no 40-80 ohms between A&B, C&D, now I have another fairly new one sitting in my bin and its showing great resistance and the distance for pintal is within tolerances, but the pintal should be able to move with fingers pressure from my understanding and it appears stuck.

??? is this normal?, for a saving of $100 bucks I'm hoping it is. Yeh, I can swap over and find out what changes if any, but why try with confusion still in my head. LOL

The pintle on the IAC may be retracted all the way, and so it can go no further.
The correct pintle length for installation is 1 1/8" I beleive - working from memory here.
If the head on the end of pintle is not the same as the IAC that's in there right now, it won't work. The pintle won't seat properly in the port.

You mentioned that oil pressure fluctuation is coinciding with your pulsating idle. You might trace the wire from the oil pressure switch (sensor) to ensure it's not grounding to anything. Also to ensure a spark plug wire is not arcing to the ops wire. Aside from the oil pressure gage, the pcm monitors the oil pressure switch. if oil pressure drops to zero, the pcm shuts down the fuel pump. I'm not positive that an intermittant signal from the oil pressure switch would fluctuate the power to the fuel pump, but it's worth a look.

This is beginning to sound more like ignition system issues. What kind of shape is your distributor cap in?