92 5.3
According to my symptoms and researching here it seems there is something up with my TPS. When my car warms up, it tries to settle into a nice idle. When it drops to that idle it surges back up, over and over. I am having trouble locating it. From some parts diagrams I have seen, I think I may be in the right area anyway. Could someone guide me closer via my pictures please. They are just different views from the pedestal. Thank you.

 

Hi, it's under the capstan. If you look at the capstan, you will see the wires from it to a connector.

 

pretty sure you mean throttle position sensor.

 

Thank you,

Isn't a capstan a marine term used for something? If so, I'm not sure where or what is a capstan from my pictures

 

You need to make sure that both throttles are set correctly and BALANCED.
The idle will 'hunt' if the throttles are not synchronized.
The black colored BOURNES TPS is NLA so you will need to find a good used or replace with the updated part if yours is the old style.

Parts TSB for you.

bob gauff

 

It's the round turntable type thingy that the throttle rods attach to.

Agreed on advice about having the throttles synchronized. This might require replacing the bushings at the bellcranks at the rear of each inlet manifold. Might as well clean the throttle bores as well and make sure the blades are set to the proper .002" gap as well.

The up-down idle can also be caused by a faulty Aux Air Valve, or any unwanted air intake. Extra air = higher idle speed. If the idle speed goes up to 1500 rpm or so, the ECU cuts off the fuel supply....which causes the idle to drop. Fuel is then turned back on, the idle goes up, and the cycle keeps repeating.

The TPS is easily checked with a voltmeter, if you have one.

Cheers
DD

 

Just a head's up.....

As of a few years ago...not sure about now....there was at least one outfit making a direct replacement for the obsolete Bourne TPS. Visually it was an exact duplicate.

I tried one and it lasted less than a year. I'd be skeptical about trying one again. Be careful if you come across one.

Cheers
DD


PS - Can't swear to it (failing memory) but I think the updated "red" TPS was standard issue on the V12s coinciding with the advent of Marelli ignition in '89. If I'm right the car in question will already have the red sensor and not need the adaptor parts.

 

I fixed my original 82 sensor, by moving sliders a little, so they hit new surface on the potentiometer. Also, I had to resolder edges of the potentiometer, so contact wires are nice and tight on them. It made a whole bunch of good difference, throttle response and entire engine acceleration curve are much better now. Two things though:
1. when motor is cold, it take a long while to warm up and for the RPM to go down to 600, I suppose it might be due to my self rebuilt idle control valve acting slow. I used Volvo Marine thermostat bulb as actuator.
2. when motor is cold and it had bad throttle response and sort of chokes when throttle applied. It does go away completely, as the motor warms up.
Any thoughts? Thanks!

 

IAC valve for certain. too lean. you could check it with a wideband O2

 

To clarify...

Do you mean it takes a long time for the coolant to get hot and show "normal" on the temp gauge?

Or are you saying it takes a long time before it starts running properly?






Either the Auxilary Air Valve isn't working right or the coolant is taking too long to get hot






"...chokes..." implies too much fuel but I'm betting it's just the opposite....too little fuel. The coolant temp sensor is the primary player in cold engine fuel control. If it's skewed hot, the ECU doesn't know the engine is cold and doesn't enrich the mixture for cold running. If you have a multimeter it's easy to check. There are other possibilities but the CTS is an easy place to begin

Cheers
DD

 

Thanks fellas, I'll get on it.

 

Where is it located, can you give me full name of this valve?

 

CTS is that temperature sensor, sitting next to left thermostat?
What are the proper readings on that?

Coolant warms up quick, it is idle valve that acts slowly.
Thanks
michael

 

Yes, just behind left thermostat

All temp readings are Deg. C and resistance is in Kilohms

0ºC 5.9 kohms
10 5.9
20 2.5
30 1.7
40 1.18
50 0.84
60 0.60
70 0.435
80 0.325
90 0.250
100 0.190

 

I think M90 is referring to an Idle Air Control Valve, probably of the type that uses a stepper motor to operate a pintle-type device to control idle speed.

If so, your car doesn't have one

The closes thing on your car is the AAV - Aux Air valve. It has an external, manually adjusted screw to control hot idle speed.

The piston inside moves up/down to admit more/less air...for controlling *cold* idle speed. The piston is operated by a temp sensitive bulb which is exposed to engine coolant.

Cheers
DD

 

I know AAV, I rebuilt it with Volvo Marine cold thermostat, it functions now, however a bit slow, it takes 4-5 minutes, for idle RPM to drop to below 900 and all the way to 600, where I like to keep it.

 

Before I start taking things apart, you know there has only been a max of 2 gallons of gas in this car since I got it. The low fuel light comes on when the car has 3.2 gallons left in the tank. I have been adding 2 gallons here and there, while warming it up and so forth. Could she be suckin fumes? Would that cause that surge?

 

Doubt it, if your fuel pump sounds even and does not change sound pitch, as it runs, you have no fuel supply issues. There is little (2 qt) fuel tank under the main tank, that makes sure you have uninterrupted fuel supply, when fuel is low and even if you decided to put your car into drift.

 

TPS is the red thing at the bottom of the turntable in the first picture

 

Figures. This car is going to sit right here for a long time if I don't figure this sporadic idle out! And that would be a shame!