Very fast idle in an '84 Mondial; bad TPS?

Don't start throwing cash at your car... check to see if the TPS is bad first.

http://ferrari.cdyn.com/carl_rose_docs/Ferrari%20328%20TPS.pdf

Bosch# 0280120310
Autozone TPS417 $69 bucks

 

I don't know about the Mondial, but the idle on the 328 can be increased if the driver pushes the floor mat up against the floor-mounted gas pedal. I experienced this when I let a friend drive the car (different driver, different orientation...). The idle went up about 2300RPM. Quick troubleshooting pointed to the floor mats....mitigated immediately.

 

Check and listen for vacuum leaks, check your vacuum hoses for puncture, crack, loose, or disconnected as they can cause idle to go higher.I don't think TPS can cause this.

 

Did you check the bimetal thermostat on you're expansion tank,make sure the leads did'nt come loose?

 

Good work, surfdoc37; I was hoping it could be a no-cost fix. It's very irritating to have an engine not idling properly. Personally, I would clean all my connectors with electronic parts cleaner and Q-tips, and exercise any mechanical devices (example, the TPS can be moved with the throttle lever). After cleaning electronic connectors, insulate them with dielectric compound (comes in a small tube). Don't forget the startup stuff like the cold start injector and warm up regulator: false signals there could cause issues even after the engine is warmed up.

Good luck.
Rob

 

Congrats on finding Autohaus AZ - I buy any/all my bosch parts there, usually for lot less than some dealer or brick and mortar place is selling them for.

Frankly, quoting $290 for a readily and widely available $50 part is shameful, if not fraudulent. All the independent shops I know absolutely do not buy generic parts such as this from the dealer. However, I do know first hand that several charge the dealer list price for a part they bought from somewhere like Autohaus AZ. Now that's just plain ripping people off......

 

How could they recommend replacement of a part that has nothing to do with a fast idle problem? An "intermittent" fast idle problem can't be "adjusted away".

No. I'd find another shop that will diagnose first, repair or replace parts second.

Good advice, but likely not the problem.

A good place to start...

Me neither!

First, it's not a Throttle Position Sensor, but rather a throttle position switch. Personally, I'd be focusing on:

-Vacuum leaks, as Mike suggested
-Throttle plate angle
-Throttle linkage at the butterfly stuck/sticking
-Throttle plate hanging up
-Throttle cable hanging up

Disconnect the throttle cable...and open and close the throttle butterfly. Does it hang up or not close completely? If so, there's your starting point...

Simple problem...and have repaired many 3x variants with this problem. I haven't repalced a TPS yet...in 25+ years.

David

 

Doesn't your '84 mondi have an auxilliary air valve ("valvola aria supplementare")? Is your AAV stuck open perhaps?

 

I agree and don't believe it to be the TPS. I would look at the cold start system and check out the thermo switch in the coolant tank. This controls the Aux. Air Valve and the cold start injector pulses. Sound like the CPU is in open loop (cold start) and not going into closed loop as the water temp rises. Need to do some more digging before you buy parts. . It just may be the AAV is open to far and not closing as the engine warms up. My 2 cents.

 

sounds like the sensitive switch on the expansion tank, it controls the vacuum solenoid to the cold start valve. when cold it holds it open increasing idle speed, once warm the valve should close. a quick simple test is to check the leads at the switch disconnect the leads and if the idle drops then you've found the problem.

also I have run into some that operate in the opposite manner, the WSM makes a bad english translation reference to it, but not enough to let you know which one you'll find.

 

Have you verified there is the proper level of coolant in the system? The bimetal strip in the aav recieves it's heat from the coolant expansion tank (valve is located below and bolted to the tank). If your system is really low on coolant, or worse totally out of coolant, the tank will not heat up due to no coolant in the tank. This would lead your aav to believe the engine is cold and cause it to be open and raise your idle. Correcting a way low on coolant situation would most likely solve both of your issues. Then you need to find why the coolant was this low in the first place.

A vacuum leak will cause a similar high idle due to the leak essentially performing the same additional airflow that the aav is designed to do.

I would bet a relatively large sum of money it is NOT the Throttle Position Sensor.

You need to find a trustworthy mechanic I'm affraid...

Spang

 

Is this light located in the bottom of the speedometer? If not, can you indicate where it is located?

Any question from the past history/paperwork that your "1984" might actually be a "1983"?

 

Well, it shouldn't be -- it should be labeled "low engine coolant level". If you check page 27 in your 308/84 OM, it is somewhat better described as "Low engine cooler level warning light". On your expansion tank there are two (independent) electric gizmos -- the level sensor for this warning light and a thermoswitch (or sensitive switch) that "tells" the injection system either:

1. "I'm cold -- so ignore the O2 sensor output, add a little extra fuel, and run open loop", or

2. "I'm warm -- so use the O2 sensor output to control the FV and run closed-loop."

So your high idle problem and this warning light always being "on" are probably not related. Also, even if the thermoswitch on the expansion tank is bad, it would only slightly alter the warm idle AF ratio (your 1984 does not have a cold start air valve like the 1980-1983 3.0L cars which can have a high idle if the thermoswitch in the expansion tank fails). As the guys have already indicated, you must have some (undesired) source that is allowing (a lot of) extra air to enter the engine -- bad AAV stuck open, cracked gasket/hose, throttle plate not closing correctly, etc.. As a very simple first test, just "pinch" one of the large rubber air hoses going to the AAV closed (simulating a closed AAV) -- if the idle drops, you've found the trouble. If not, you'll have to keep looking for another air leak. Good Hunting!