Idle is high on 4.0l

[88justin]

I've been trying to get this high idle figured out.
-'88
-4.0l
-peugeot
-Replaced the IAS
-Callibrated the TPS to 4.2V/4.8V, lowers voltage smoothly when actuated.
-cleaned sensor electrical terminals

, yet i still get an irregular idle. when i start the engine, the idle is fine. then after driving a while it rises and stays at 1500rpm. and a little while later it almost always ends up at 2000rpm. at that point if i turn it off and restart, it revs at a constant 3000rpm and doesnt come down till i let it rest a bit with the ignition off.

anybody have any ideas? the jeep sounds like a beast with flowmasters and a constant 2000 rpm idle, but its getting anoying and i ran out of ideas.

thanks

[PaulJ]

Sometimes the C101 connector can be a problem. All the engine control wiring passes through it. It a big connector hanging off the firewall just above the brake booster. It's full of very sticky grease that's hard to clean up.

[satan]

Just for fun 88justin, why did you set the TPS to the atuomatic tranny specs? You indicate that you have a Peugot tranny (since the auto is AW, it'd follow that your XJ is 5-speed equipped and therefore only has qty=1 TPS connection)...

The Renix ECU is not as adaptable as the later ChryCo computer systems and instead is looking for something more like 0.8V from pin C (when referenced to the ECU Sensor ground, which should be pin B).

For my part, I'd recommend verifying that your TPS pin B is providing a good ground, and that with key on and throttle closed that pin C reads 0.8V (+0.0/-0.2)

Checking C101 does have it's value as well, to assure yourself that C101 is causing you havoc -- verify the TPS readings as measured from the ECU. On the ECU,:
* pin A of the TPS is ECU pin c-15 and should have a constant 5V signal;
* pin B of the TPS (the sensor ground) arrives at the ECU at pin d-3; if this is bad you can add another ground at/near the TPS);
* pin C of the TPS (the output voltage) arrives at the ECU on pin c-7

So, key-on throttle closed - ECU c-7 should show 0.8V, and c-15 should show ~5V when measured using d-3 as a ground reference. (if you measure at the ECU after setting the TPS output, you can confirm the connections running through C101)

[assterisk]

i had a similar problem..... check your i.a.c motor......
replaced mine and it works fine now......

[88justin]

Thanks for the test procedure. i found it interesting that my chiltons manual pictures a TPS with one connector for the manual and one with two connectors for teh auto. I assure you i have the 5-speed , but my TPS has two connecotrs?! they're both plugged in.
also it mentions that the output signal from the TPS should increase in voltage as the throtttle is opened,yet my TPS measures 4.2V and decreases when the throttle is opened.

what is going on?

thanks

[satan]

Yeah - chilton's does that -

The 4.2 that you're reading is from pin A to pin C (from the output to the source voltage...) -- so you're reading the difference there instead of the ground referenced value they talk about increasing with throttle opening...

You'll only wanna read the ECU connector for the 5-sp (not uncommon to see the auto one hooked-up in there, they're sometimes cheaper and seem to be more available - and if you stock the Auto one it'll work in BOTH applications) - the flat connector is all you're looking for data from --

Look to ensure that it has good ground on pin B -- the ReixII looks for just a little over 0.7V and the ECU returning from pin C to enter into the idle mode ...

... While the 4.2 volts you're reading is in keeping with pin C presenting 0.8 (ground reference) Volts at idle... IF your ECU's regulator is pushing out 5.2 volts - the your ECU will see 1.0 Volts with no throttle applied and you may not get the idle you're wanting... Additionally, if the ground at that sensor is high then your output may be consistantly high as well...

The Chilton book (as many are) is written by referencing the factory manual - there's a great deal of pressure to release the books as quickly as possible - which usually means that the chilton manual's include all of the factory original maual faults (the factory corrects theirs much of the time with updates sent to dealers and all, but Chilton's already printed thousands, which exist in general circulation with no revision controls...)



Originally posted by 88justin
Thanks for the test procedure. i found it interesting that my chiltons manual pictures a TPS with one connector for the manual and one with two connectors for teh auto. I assure you i have the 5-speed , but my TPS has two connecotrs?! they're both plugged in.
also it mentions that the output signal from the TPS should increase in voltage as the throtttle is opened,yet my TPS measures 4.2V and decreases when the throttle is opened.

what is going on?

thanks

[88justin]

OMG, thank you so much!

ill try to get it calibrated at the ECU connection and see how things are.

....peace