Issue or normal?

[Vengence]

When I start my car, it starts up right away and no issue there, however, After I start the PT the engine revs at about 1200 rpm, goes down to 1000 rpm, jumps back up to 12-1300 rpm, back down to 1000 rpm, then up to 11-1200 rpm, then stays around 1000 rpm until the engine warms up and idles at about 6-650 rpm.

I have never seen any car or previous PT's do this.....Is this normal or is there something wrong?

[dsab]

The throttle position sensor may be defective.

[ptcruisersteve]

Is your engine light on? If so what is the engine trouble codes you are getting?

[Vengence]

Sensor is possible and no engine light or codes.

[Handy_Cruiser]

A bad TPS usually throws a code. But likely deserves looking at.

Beyond that, you may want to check the Idle Air Control (IAC) valve. If me, I'd remove it and clean it very well. I'd also check the ohms reading across the two terminal. They should be 7.3-13 ohms in most cases and the plunger should move freely. A sticking IAC valve doesn't always throw a code.

Some items that might cause your symptoms include:

TPS
IAC valve
MAP sensor
Intake manifold leak
Bad PCV valve
Weak fuel pump
Engine miss and/or bad plugs/plug wires

[rob302]

I would leave it alone. If a problem gets worse you'll know what wants attention

[wb2kki]

Also check throttle body if a lot of carbon may need to be cleaned as well as the map sensor and as mentioned IAC.

NOTE: Make sure you use the right cleaner or you can cause more harm than good.

Run a good cleaner in the gas tank maybe not a bad idea.

Also might check for a vacumm leak.

Good luck.

[Vengence]

Originally Posted by Handy_Cruiser

A bad TPS usually throws a code. But likely deserves looking at.

Beyond that, you may want to check the Idle Air Control (IAC) valve. If me, I'd remove it and clean it very well. I'd also check the ohms reading across the two terminal. They should be 7.3-13 ohms in most cases and the plunger should move freely. A sticking IAC valve doesn't always throw a code.

Some items that might cause your symptoms include:

TPS
IAC valve
MAP sensor
Intake manifold leak
Bad PCV valve
Weak fuel pump
Engine miss and/or bad plugs/plug wires

TPS- will look into
IAC valve- will look into
MAP sensor- will look into
Intake manifold leak- likely....However, I had all 16 valves replaced and engine resurfaced when I had low compression a few months back....Could this still be an issue with that being done?
Bad PCV valve- will look into
Weak fuel pump- Also likely......About a month ago, I was driving where it was stop and go traffic going to a gas station (I was just below 1/4 tank) and the car felt like it was going to stall....RPM's dropped to about 400 and went back up and dropped one more time and went back up and ran fine from there.

[Vengence]

Originally Posted by wb2kki

Also check throttle body if a lot of carbon may need to be cleaned as well as the map sensor and as mentioned IAC.

NOTE: Make sure you use the right cleaner or you can cause more harm than good.

Run a good cleaner in the gas tank maybe not a bad idea.

Also might check for a vacumm leak.

Good luck.

Vacuum leak is one thing I considered as well at first......

Also I should mention that most of the time when filling the gas tank I cannot fully hold the handle to fill at full speed.....If I do the pump shuts off.

[rob302]

i would say FOR SURE you can skip the TPS, as without a code, it IS working correctly and the value it's reporting at idle is AOK.

i would also say you could FOR SURE skip the fuel pump. a weak fuel pump would be much more likely to be a problem at speed. a failing one usually causes you to stall and not restart unless you bang on the tank

the ISC (idle speed controller) is used for IAC(idle air control). this you can simply unhook the connector on a few seconds after you start the car cold. if the idle is still fluctuating, it is due to timing/fueling changes, as instant idle is corrected more by timing than anything else. this IMO would point to sensors reporting incorrectly, bad MAP, o2's reporting bad info, shady ground, etc.

IMO it's likely one of the sensors or their grounds.. since idle will drop when warm. nitro seems to like unhooking and reseating connectors. maybe try that first?

the ECT sensor should be questioned as well. the value the ECT reports at startup does change my ISC position and just based on reported temp it can modify the idle by 500 rpm. if the idle fluctuation goes away when you unhook the ISC, you might inspect the temp sensor and its ground as well.

...or just wait until the problem becomes a problem, and is easier to diagnose and fix.

i've gotten fairly good at idle tuning, as the setup i use on my ford required me to study idle for several weeks, first time i read it it may as well have been in chinese. https://eectuning.org/forums/viewtopic.php?t=17439