TPS (throttle position sensor) Symptoms

[Smiliesafari]

OK, so it's heat related. Could be failing coil or failing ignition module.

[potskie]

funny i have similar symtoms i'm going to be checking the TPS today the TB will wait for another day when i get rid of the restrictor in there.... :-k

Mines doing the same thing except it's doing it when I'm not on the throttle as well. Pump also sounds knarly.... Hence the replacement how to you guys will be seeing. If that doesn't fix it then I'll just start throwing mad parts at it lol. Already checked the rotor and cap and ignition module on mine and they were top notch.

[AstroManiac]

OK... here's an update on my buddy's 98 Astro AWD 4.3 "W"... a couple days ago, he changed the oil & filter & discovered a small leak at the adapter the oil cooler lines come off between the block & filter.
He changed the fuel filter, which had about 20,000 miles/18 months on it & it was clean & clear.
I helped him & we removed the engine cover & re-checked everything.
We actually ran the engine for about 2 1/2 hours & though it warmed up, it still ran great... no hesitation! We drove it around the block several times & out onto the freeway @ 65 mph for about 6 miles & it ran great!
With the engine sitting & idling, we re-installed the engine cover/dash! He gets behind the wheel to move the van & the hesitation is back!
If you just "hit the gas", the engine would die out & you could hear a little "pop" that sounded to be in the intake manifold.
Still NO CODES!!!
We pulled the engine cover back off to see if any wires or anything were being pinched, but everything looked great!
The hesitation was still there.
We let it sit for about 3 hours to cool down & started it again.
Once again it ran great until it warmed up & the hesitation came back!

We read in the Chilton's manual that the fuel pressure needed to be between 51 psi to 59 psi & in another manual it says 55 psi to 62 psi!
With my fuel gauge it reads 55 psi at idle & when you hit the gas it goes up to 60 psi for a moment, then drops down to 54-55 psi.
With the transmission in Drive, the fuel psi drops to 51-52 psi, which the Chiltons says is normal.
We clamped off the return line & the pressure rose to 62-63 psi.
With the engine off, the fuel pressure holds for at least 20-30 minutes.
When the pressure is gone & you turn on the key switch, the pressure only rose to about 25 psi. Cycle the switch again & it would rise to about 40 psi. Cycle it a 3rd time & it would rise to 55 psi.
The fuel pump is 2 years old & has about 30,000 miles on it.
My sense tells me that the pump is weak, but why does the engine run so well when it is cold???
The pumps psi is the same whether it is cold or hot!

We've checked the coil etc. as per what we found on Google & everything checks out!

Now we're really confused!
Any ideas???

Ventura County, CA
98 Astro AWD 4.3 "W"

[Cobra]

i can't really remmebr well but shouldn't the fuel pressure stay up for longer then 30 mins.....? i don't think it should hit 0 in under 12 hours i might be wrong tho (probably am) but i think that was a sign of a problem with the fuel pressure reg...?

[mikedamech]

Get a OEM fuel pump, or NoAutoPartsAvaible Assembly. When the pump only goes to 40 on the first cycle it's time for a Very expensive pump.

[mikedamech]

We checked the TPS & it works fine. We also checked the MAP & it is OK according to the test.
This morning, it fired up & ran great... UNTIL... it warmed up & then the hesitation/die-ing was back.
Warmed up it still idles great, but any movement of the throttle pedal & it hesitates or dies.
No codes!
Is there a "temp sender" we need to check???

The only way you can check a TPS is with a DSO lab scope, the sampling rate of a DVO meter is way too slow to catch a glitch.

[AstroManiac]

My buddy went ahead & replaced the TPS today & "no change" everything is still the same.

[AstroManiac]

Well... my buddy & I didn't touch his 98 Astro AWD w/ "W" engine for several months.
We started it the other day & had to give it a shot of starting fluid to get it to start & run. With the engine cover off, it idled & ran great & we drove it about 50 miles! Got back to the shop, parked it in front of the garage & with it idling, re-installed the engine cover!
In about 8 minutes, it started its hesitation/dieing thing again!
I had bought a "fuel pump repair kit" off Ebay for him, so we dropped the tank & though it took a couple hours, finally got the new pump & screen installed! re-installed the tank & checked all connections etc. & everything was perfect!
We hooked up the fuel pressure gauge, turned the key & the pressure went to 60 psi, cranked it, pressure stayed the same, but it would not start, unless we gave it a squirt of starting fluid!
My buddy said we were going to get it to run properly even if it put him in the poor-house!
We went to the Chevy dealer & bought another GM cap, rotor, AC plugs, plug wires, temp sensor, temp gauge sender, ignition coil, TPS, MAP sensor, ICM/Ignition Control Module & a new Cam Position Sensor for the distributor!
We installed everything & put the engine cover back in place! Cleaned the van up & put all of the tools away!
He got into the driver's seat, put the key into the ignition switch & turned it to start!!!
The van started immediately!!! We sit there warming it up & it kept running great!!! After it was thoroughly warmed up, we backed out of the driveway & went to the gas station as there was only a couple gallons of gas in it! After putting in 10 more gallons of 87 octane, now 12 total in a 27 gallon tank,, we headed out for an extended test drive!
The van had never run better! Great power & the fuel mileage seemed to be a bit better too!
We put 240 miles on her of which 50 miles or so was in town/city driving & she never missed a beat!!! Fuel mileage averaged right at 20mpg!!!
So what ever the problem was, is now apprently gone, but we sure wish we knew what it was!!!
We also fixed the oil leak by the oil filter, that was a bad gasket between the adapter & the block!
Hurrah for now!!!

98 Astro AWD "W" engine, 208,000 miles
Ventura County, CA