1987 TBI 305 problems. HELP!

[badbowtie89]

I bought a 1987 Chevy v10 with a throttle body 305 from the car dealership I work at. Within a week I already had to replace the clutch. I pulled the engine out to do this (I know it was harder this way)
When I put the engine back in, I ran it and it Service engine soon light came on. I read the codes and it came back with code 22 "low voltage at throttle position sensor" I replaced the TPS and it ran fine. The next morning I go to start it and it idles high then drops down to about 500 rpm and the SES light comes on. I decided to drive it and it would randomly cut out while driving at low rpm. Once it got warm the SES shut off and it ran fine. Once I stopped I read the codes and it comes up with code 21 "High voltage at throttle position sensor".
I'm confused on what this means? The sensor is new and everything. It just runs like **** until it gets warm.
Any help or advice is appreciated!
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[bigblue87]

Not really sure what the problem might be other than the connection being bad. although im sure you checked it several times.

All i can say for sure is that these trucks want your blood, sweat, tears and respect before they are nice to you.... and i learned that the hard way.

Other than that maybe the idle is the idle air control?
or maybe something isn't grounded correctly?

[rfmaster]

Originally Posted by badbowtie89

I bought a 1987 Chevy v10 with a throttle body 305 from the car dealership I work at. Within a week I already had to replace the clutch. I pulled the engine out to do this (I know it was harder this way)
When I put the engine back in, I ran it and it Service engine soon light came on. I read the codes and it came back with code 22 "low voltage at throttle position sensor" I replaced the TPS and it ran fine. The next morning I go to start it and it idles high then drops down to about 500 rpm and the SES light comes on. I decided to drive it and it would randomly cut out while driving at low rpm. Once it got warm the SES shut off and it ran fine. Once I stopped I read the codes and it comes up with code 21 "High voltage at throttle position sensor".
I'm confused on what this means? The sensor is new and everything. It just runs like **** until it gets warm.
Any help or advice is appreciated!
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Check the ground wire lead (Pin A, black wire) of the TPS is not damaged and connected to the ground lug in the back side of passenger cylinder head (3/8" bolt). Also, it is very common to damage 20+year old harness during engine R&R, things get brittle with age. Make sure that front harness ground lug is bolted down tight near thermostat housing. Loose or missing ground straps will play havoc on any EFI system.

//RF

[badbowtie89]

Originally Posted by rfmaster

Check the ground wire lead (Pin A, black wire) of the TPS is not damaged and connected to the ground lug in the back side of passenger cylinder head (3/8" bolt). Also, it is very common to damage 20+year old harness during engine R&R, things get brittle with age. Make sure that front harness ground lug is bolted down tight near thermostat housing. Loose or missing ground straps will play havoc on any EFI system.

//RF

Thanks! I will check out that ground wire. As for the front harness ground I messed with that a lot and didn't notice any difference
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[badbowtie89]

I checked all the wiring and it is all fine. I cleaned all the grounds off as well.
I started it this morning and it ran rough(code 21), I drove to work and it would hiccup every now and then. Once it got to operating temperature, it ran fine and SES went off. I drove it home on my lunch break and it ran normal with no SES?

It's obviously temperature related. What else could it be?
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[rfmaster]

Originally Posted by badbowtie89

I checked all the wiring and it is all fine. I cleaned all the grounds off as well.
I started it this morning and it ran rough(code 21), I drove to work and it would hiccup every now and then. Once it got to operating temperature, it ran fine and SES went off. I drove it home on my lunch break and it ran normal with no SES?

It's obviously temperature related. What else could it be?
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Code 21 - TPS voltage high is set when TPS voltage is above 2.5 volts for 2 seconds while the MAP sensor is below 60 kPa with engine speed is less than 1800 RPM. The fact that things rectify themselves once engine bay heats up indicates intermittent connection..

Basic electrical checks require DVM.

1) Ground circuit check, engine bay cold, Engine off, ignition off. Disconnect TPS plug from TPS sensor. Set DVM to read OHMS. Measure resistance between Pin A (black wire) and good electrical ground - should be 0.1 to 0.8 Ohms depending on probe contact resistance and ground circuit connections. Anything above 10 Ohms would indicate a broken or intermittent wire in this ground circuit. Repeat after after driving - engine bay hot.

2) + 5 volt reference circuit check, engine bay cold, engine off, ignition ON.. Set DVM to read DC volts. Measure voltage between Pin C (gray wire) and good electrical ground. You should see between 4.85 and 5.15 Vdc - most of the time I see 5.0 V right on the spot.

It is common for TPS plug pins to wire connection to develop intermittent. The connection is crimped when it was assembled by GM, but after 20+ years of service may have resulted in oxidation at this junction. Also, wire gets strained when routed away from the TPS resulting in a frayed wire strands within wire insulation jacket. With engine cold, TPS plugged in, gently move this circuit while observing engine performance - if you spot a jump in engine RPM you've found a broken wire....

Brand new TPS's (non GM) are also known to be faulty or intermittent straight out of the box!!

//RF

[badbowtie89]

Originally Posted by rfmaster

Code 21 - TPS voltage high is set when TPS voltage is above 2.5 volts for 2 seconds while the MAP sensor is below 60 kPa with engine speed is less than 1800 RPM. The fact that things rectify themselves once engine bay heats up indicates intermittent connection..

Basic electrical checks require DVM.

1) Ground circuit check, engine bay cold, Engine off, ignition off. Disconnect TPS plug from TPS sensor. Set DVM to read OHMS. Measure resistance between Pin A (black wire) and good electrical ground - should be 0.1 to 0.8 Ohms depending on probe contact resistance and ground circuit connections. Anything above 10 Ohms would indicate a broken or intermittent wire in this ground circuit. Repeat after after driving - engine bay hot.

2) + 5 volt reference circuit check, engine bay cold, engine off, ignition ON.. Set DVM to read DC volts. Measure voltage between Pin C (gray wire) and good electrical ground. You should see between 4.85 and 5.15 Vdc - most of the time I see 5.0 V right on the spot.

It is common for TPS plug pins to wire connection to develop intermittent. The connection is crimped when it was assembled by GM, but after 20+ years of service may have resulted in oxidation at this junction. Also, wire gets strained when routed away from the TPS resulting in a frayed wire strands within wire insulation jacket. With engine cold, TPS plugged in, gently move this circuit while observing engine performance - if you spot a jump in engine RPM you've found a broken wire....

Brand new TPS's (non GM) are also known to be faulty or intermittent straight out of the box!!

//RF

I replaced the TPS connector plug, (haven got my hands on a DVM yet).
It still idles low and rough when cold, while driving at low rpm it hiccups/sputters off and on. Once again it gets better when it's warm
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[badbowtie89]

Thanks! I'll try those things and post back tomorrow
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