No Start (Possible TPS)

I left for work this morning and the Jeep (97 4.0/Auto) started normally. I drove about a mile to the gas station and put gas in. After that, it wouldn't start. It would crank fine, but no start. I discovered that if I gave it some gas, it would start and die. If I stayed on the gas, it would run as long as I didn't let off the gas.

I was already running late for work, so I drove it with 2 feet back to my house and jumped in another car. I'm planning on pulling the codes when I get home from work.

I find it odd, that it would start and run fine until I turned it off. Also, as 2 foot notes, it's very foggy and damp this morning and it's been raining pretty good for the last day or two. I also removed the mechanical fan shroud the other night to do some eyeball measurements for a Taurus fan swap, and have not driven it since then.

Lastly, if it is the TPS, is there a way to clean or adjust it. I really don't want to have to buy a new one.

those symptoms sound somewhat like a fuel delivery problem. I had a 99 that started acting up like that and it ended up being the fuel pressure regulator, and the bad news is that the fp reg is part of the fuel pump assembly.

a bad or out of spec tps wont stop it from starting. a bad cps will keep it from starting.

other possible problems could be fuel related. also if you need to keep on the throttle to keep it running, i would clean the throttle body and iac along with checking the battery voltage. a weak battery or bad connections can cause the engine to run bad at start-up when trying to idle.

89xj said:

a bad or out of spec tps wont stop it from starting. a bad cps will keep it from starting.

other possible problems could be fuel related. also if you need to keep on the throttle to keep it running, i would clean the throttle body and iac along with checking the battery voltage. a weak battery or bad connections can cause the engine to run bad at start-up when trying to idle.

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Hmmm...thanks for the help. The PO replaced the positive battery terminal and did a very poor job. I wonder if (while driving this morning), water could have dripped in under the hood, and caused just enough resistance to cause my issues.

$5 for a new set of battery terminals is way better than a TPS, CPS, or a fuel pump assembly.

dagr8tim said:

Hmmm...thanks for the help. The PO replaced the positive battery terminal and did a very poor job. I wonder if (while driving this morning), water could have dripped in under the hood, and caused just enough resistance to cause my issues.

$5 for a new set of battery terminals is way better than a TPS, CPS, or a fuel pump assembly.

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it could be a battery(charging) connection problem just from the moist humid air or from corrosion, it doesnt have to have direct rain water to cause the problem, if indeed this is your problem.

dont just replace parts because you think its the problem, test your charging system along with the tps and cps with a voltmeter, not the voltage gauge on the dash.

If the IAP picked up carbon when you shut it off, the idle would definitely be affected. Spray it out and clean it.

Check that the PO didn't mess with the throttle screw on the body and turn it down to the point all air had to come out the Idle Adjuster.

TiRod said:

If the IAP picked up carbon when you shut it off, the idle would definitely be affected. Spray it out and clean it.

Check that the PO didn't mess with the throttle screw on the body and turn it down to the point all air had to come out the Idle Adjuster.

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Thanks, being a Ford guy, I'm not familar with the IAP. Is that Jeep's version of the IAC (Idle Air Controler)?

Also, could you give alittle more instructions on adjusting the throttle screw. Once I get it running, do I just adjust it down to where it idles at about 600 to 700 RPM's?

Lastly, this thing has run spot on since Feb with no major issues. I will stop and grab a can of intake cleaner when I get off work this afternoon and spray some things out.

adjusting the idle screw is the last thing you want to do and should be done only if all the electrical and mechanical components of the fuel injection/charging system have been ruled out as a problem.

if it has been running spot on since feb, i doubt the idle adjustment screw needs to be adjusted. something is not operating as i should, you need to test/inspect/clean. a problem like this can get expensive if you just throw parts at it.

Jeep has the IAC, just like Ford. That is your most likely culprit, and just like on Fords can be cleaned and tested to make sure the pintle moves. And like 89xj said, if it worked good recently, don't mess with the idle adjustment screw on the throttle body. Make sure the connection to the IAC is good too. I'm not so sure about the TPS not affecting starting. On my Ford CV, with problems just like that starting, it ended up being the TPS. You can check it with a voltmeter. Input should be 5 volts and output at idle should be 0.26V.

winterbeater said:

Jeep has the IAC, just like Ford. That is your most likely culprit, and just like on Fords can be cleaned and tested to make sure the pintle moves. And like 89xj said, if it worked good recently, don't mess with the idle adjustment screw on the throttle body. Make sure the connection to the IAC is good too. I'm not so sure about the TPS not affecting starting. On my Ford CV, with problems just like that starting, it ended up being the TPS. You can check it with a voltmeter.

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Thanks for the suggestions. I think my first step is to spend some quality time with a can of contact cleaner & intake cleaner. I'm going to try all of my plugs on the TB and make sure they are clean.

The reason I'm thinking TPS is that I had an old Tempo that pretty much acted the same way when the TPS went bad.

winterbeater said:

Jeep has the IAC, just like Ford. That is your most likely culprit, and just like on Fords can be cleaned and tested to make sure the pintle moves. And like 89xj said, if it worked good recently, don't mess with the idle adjustment screw on the throttle body. Make sure the connection to the IAC is good too. I'm not so sure about the TPS not affecting starting. On my Ford CV, with problems just like that starting, it ended up being the TPS. You can check it with a voltmeter. Input should be 5 volts and output at idle should be 0.26V.

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dagr8tim said:

Thanks for the suggestions. I think my first step is to spend some quality time with a can of contact cleaner & intake cleaner. I'm going to try all of my plugs on the TB and make sure they are clean.

The reason I'm thinking TPS is that I had an old Tempo that pretty much acted the same way when the TPS went bad.

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were those ford engines MAF(mass air flow) or MAP(manifold absolute pressure) regulated? on the 4.0 that is MAP, i dont thnk the tps would cause a no start. you can unplug the tps on my 89 renix 4.0 and it will still start.

89xj said:

were those ford engines MAF(mass air flow) or MAP(manifold absolute pressure) regulated? on the 4.0 that is MAP, i dont thnk the tps would cause a no start. you can unplug the tps on my 89 renix 4.0 and it will still start.

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This was an 88 2.3 OHV HSC motor with a MAP system. It would turn over, and fire for a split second and die.

The manual does say that the TPS is monitored by the PCM for start. It's easy enough to check with a voltmeter anyway.

I got home from work this afternoon, and the code were 12 & 55 based on the CEL & the digital odometer. Just for S&G I tried to start it, and it started up fine. I drove it around the block afew times until the dash temp gauge was reading 210.

I brought it back home and pulled the codes again. I got 12, 45, & 55. What makes this even more odd, is that the PO removed the rear cat & rear 02 sensor. Last time I checked the codes, I got 12, 21, & 55.

Does anyone have any suggestions based on this information?

A bad TPS on my 93 gave me the symptoms yours has. A new TPS solved the problems nicely. My brother had similar problems with his 91, but he had a new TPS in it already so we checked his CPS and it was shot so a new CPS solved his problems... those are where'd I'd start if I were you.