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post #1 of 6 (permalink) Old 07-03-2006, 12:22 PM Thread Starter
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RPM fluctuates TPS ohms or volt readings

I have a 1999 Intrepid, 2.7 which is having problems with RPM fluctuations, and I believe it could be the TPS sensor. I tested the resistance of the power (VT/WT) and sensor ground (BK/LB), it reads 4.2 ohms (good so far). Then I tested the sensor signal (OR/DB) and sensor ground (BK/LB), it reads .5 ohms (good so far), then I gradually opened the throttle to WOT, it reads, 3.0 ohms (not good, I think). So I decided to check the volts. The volts of the power and sensor ground reads 4.9 volts (good so far), then checked the volts on the sensor signal with the ground on the car, it reads .6 volts (good so far), then while gradually opening the throttle to WOT position, it reads 3.7 volts (not good I think). In my Haynes Manual it states “gradually open the throttle – the voltage should increase smoothly to approx. 4.5 volts at wide open throttle. If test results are incorrect, replace TPS.”

Now here’s my dilemma: since the manual covers different models and engine sizes, I called the dealership to see if there was specifics regarding the volt ratings for my car (forgive me if this seems foolish, but this is my first experience in troubleshooting a vehicle, I am only beginning to learn through this forum, the FSM, and my Haynes Manual). Anyway, the mechanic says that 3.7 volts seems about right. So now I’m confused, is the book correct or is the mechanic? Could someone please tell me what the proper ohms or volt readings for the TPS are? Is the sensor bad? Does it need to be replaced? I have already put too much money into “false” repairs (replacing sensors, fuel injectors, etc.) diagnosed by mechanics. Your insight would greatly be appreciated.
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post #2 of 6 (permalink) Old 07-03-2006, 12:43 PM
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Quote:
Originally Posted by dgirardin
I have a 1999 Intrepid, 2.7 which is having problems with RPM fluctuations, and I believe it could be the TPS sensor. I tested the resistance of the power (VT/WT) and sensor ground (BK/LB), it reads 4.2 ohms (good so far). Then I tested the sensor signal (OR/DB) and sensor ground (BK/LB), it reads .5 ohms (good so far), then I gradually opened the throttle to WOT, it reads, 3.0 ohms (not good, I think). So I decided to check the volts. The volts of the power and sensor ground reads 4.9 volts (good so far), then checked the volts on the sensor signal with the ground on the car, it reads .6 volts (good so far), then while gradually opening the throttle to WOT position, it reads 3.7 volts (not good I think). In my Haynes Manual it states “gradually open the throttle – the voltage should increase smoothly to approx. 4.5 volts at wide open throttle. If test results are incorrect, replace TPS.”

Now here’s my dilemma: since the manual covers different models and engine sizes, I called the dealership to see if there was specifics regarding the volt ratings for my car (forgive me if this seems foolish, but this is my first experience in troubleshooting a vehicle, I am only beginning to learn through this forum, the FSM, and my Haynes Manual). Anyway, the mechanic says that 3.7 volts seems about right. So now I’m confused, is the book correct or is the mechanic? Could someone please tell me what the proper ohms or volt readings for the TPS are? Is the sensor bad? Does it need to be replaced? I have already put too much money into “false” repairs (replacing sensors, fuel injectors, etc.) diagnosed by mechanics. Your insight would greatly be appreciated.
The main thing to check is that the voltage increases Gradually and evenly(smothly) as you open the throttle. Your readings are a little low according to the manual, but if they increase smothly it shouln't cause RPM fluctuations.
When do the RPMs fluctuate ? at idle? Full throttle? There are a lot of other sensors that control engine RPMS also.
Did you check for diagnostic codes?
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post #3 of 6 (permalink) Old 07-03-2006, 01:10 PM Thread Starter
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Yes, the voltage does increase gradually and smoothly. The RPMs begin to fluctuate at 1900 and up, the needle jumps all over the place. It only happens while accelerating, and fluctuates more rapidly when going up an incline. Although I don't drive with cruise control, I did test to see if the symptoms where the same (they were). I personally have replaced the PCV valve and hose (there was sufficient carbon buildup). I attempted to take off the EGR valve, and hoses and in doing so the bolts broke off. So now the piece is in the machine shop waiting to be re-tapped. I checked the resistance on the EGR valve/solenoid, readings were within spec. I also cleaned the hose to the manifold, it was half plugged. The spark plugs checked out fine. I also checked the vacuum at the intake/pcv and the reading was 19 Hg.

As well the garage has, changed the input speed sensor, the crankshaft and cam sensor, the fuel pump, spark plugs, and cleaned the fuel injectors. As well, the oil, coolant, and trannmission have all been flushed.
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post #4 of 6 (permalink) Old 07-03-2006, 01:15 PM
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Now this is a true story--
I've been experiencing some rpm stutter, and been meaning to clean the IAC-(intake,or idle air control, I believe). 89 octane helped somewhat, so I got lazy and put a bottle injector
cleaner in the tank this morning.
Never 'cleaned' the injectors before, but it made a world of difference in less than 20 miles! Smmooooth as can be- and it wasn't Seafoam-couldn't locate it.
Anyway, have you read the diagnostic codes from your odometer yet?

Last edited by alarkyokie; 07-03-2006 at 01:18 PM.
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post #5 of 6 (permalink) Old 07-03-2006, 01:33 PM Thread Starter
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Even though the fuel injectors were cleaned (Dec. 2005), I thought maybe it could need another cleaning. Twice within the last month, I have put fuel and system cleaner in the gas tank. As well, I put in a bottle of 'water removal' in the tank. I didn't help. I have also taken off the IAC sensor (idle air control), the ohms readings were 54 ohms (within spec). Although it didn't look that bad, I cleaned it up. I haven't been able test drive the car yet because I am waiting on my EGR valve/solenoid to come back from the shop.
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post #6 of 6 (permalink) Old 07-03-2006, 02:01 PM Thread Starter
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Sorry, in regards to codes coming up. The engine light doesn't come on when this happens, so I don't get any codes, except the generic 1684. Although, a couple of weeks ago, and I ashamed to say this, instead of putting the car in drive, I accidentally put it in 3rd gear. This time the RPMs really jumped all over the place and the car was stuttering/hesitating with a jerking motion, most times when the RPMs fluctuate the car just lulls back and forth. The engine light did come on after this. The codes that came up were 0352 and 0355. I disconnected the battery, erased the codes and they have not come up again since.
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