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Shifting into reverse cures high idle - WTF? by yellowstone
Started on: 07-21-2013 01:39 PM
Replies: 16 (609 views)
Last post by: yellowstone on 12-11-2013 02:42 PM
yellowstone
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Report this Post07-21-2013 01:39 PM Click Here to See the Profile for yellowstoneSend a Private Message to yellowstoneEdit/Delete MessageReply w/QuoteDirect Link to This Post
I've had an issue for a few weeks that after driving for a while, the car starts idling fast (around 2,000 RPM instead of the usual 700). For a while I could just tap the accelerator and that would make the idle come down to normal. Now that doesn't work anymore but I found that if I shift into reverse, the engine will immediately start to idle normally again, even when I use the forward gears again. That doesn't make any sense to me - ideas?

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La fiera
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Report this Post07-21-2013 01:42 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
Check your mounts, throttle body spring. Also on the firewall there is a filter for the brake booster, check it and see if it is melted.
Disconnect the brake booster and plug the hose and see what happens, this way you are also testing if the brake booster has an internal leak.

[This message has been edited by La fiera (edited 07-21-2013).]

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Lou6t4gto
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Report this Post07-21-2013 02:08 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
sounds like a mount. when you shift into reverse, the engine twists and loosens up the throttle cable ?
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yellowstone
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Report this Post10-14-2013 06:47 PM Click Here to See the Profile for yellowstoneSend a Private Message to yellowstoneEdit/Delete MessageReply w/QuoteDirect Link to This Post
I finally connected the scantool and got some more insight into this issue. I had a code 15 (coolant sensor voltage) set and the SES light came on during idle when I first started it up but then went away.

Whenever the engine starts to idle high and stumble on acceleration, the coolant temperature will drop instantly, from 208 degF (when warm) to something like -13 and 37 deg F. At the same time, the IAC reading will go from 70 to 170 or 180.

However, when I shift into reverse, the RPMs will come down immediately and go back to normal.

Here's the data for such a cycle (normal operation, surge, shifting into reverse, normal operation):



I think that's very odd - ideas? Change coolant sensor?

At the same time the oil pressure gauge reads zero and the oil pressure warning light is on but the engine has enough oil (I check before every drive).

[This message has been edited by yellowstone (edited 10-14-2013).]

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Bloozberry
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Report this Post10-14-2013 09:27 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by yellowstone:
Change coolant sensor? At the same time the oil pressure gauge reads zero and the oil pressure warning light is on but the engine has enough oil (I check before every drive).


It's not surprising you get some of the results you're seeing given that the coolant temp signal is unreliable. According to the FSM, the coolant temp sender input is used to control fuel delivery, spark timing, IAC, TCC, and EGR. I suspect it's a wiring issue and not a sensor problem, though it should be easy enough to check. At normal operating temp you can back-probe the coolant temp sender with a volt meter and you should get between 1.5V - 2.0V. Check it (if you can) when the engine is misbehaving that way you'll be able to figure out if the sender is operating correctly or not, and if it is, then you've isolated the problem to a wiring issue between the sender and the ECM.

BTW, I checked the FSM to see if the two circuits were interconnected in any way (oil pressure & ECM coolant temp sender) but they don't appear to be, so I suspect they are independent problems.

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Marvin McInnis
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Report this Post10-15-2013 11:50 AM Click Here to See the Profile for Marvin McInnisClick Here to visit Marvin McInnis's HomePageSend a Private Message to Marvin McInnisEdit/Delete MessageReply w/QuoteDirect Link to This Post
It sounds to me, too, like a wiring problem. Be sure to check the engine-to-chassis ground strap(s) before you start replacing parts.

[This message has been edited by Marvin McInnis (edited 10-15-2013).]

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Report this Post10-24-2013 02:25 PM Click Here to See the Profile for spadClick Here to visit spad's HomePageClick Here to Email spadSend a Private Message to spadEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hello Yellowstone,
Do you have auto or manual transmission. That would help a bit, since auto trans makes load to engine while reverse gear is selected.
Are those scantool data temperatures in degrees celsius or fahrenheit?
~96 'C would make sense for coolant, but I doubt MAT would be ~60 'C at the same time.

Coolant temperature sensor (CTS) is the one we need to track. It has common ground with TPS. Since we do not see TPS go high at the same time, we know ECM D12 wiring (common ground) is ok.
CTS has following temperature ('C) vs resistance curve: http://spad.dy.fi/temp/coolant_temp_sensor.png

At your case temperature drops, so I guess:
-ECM C10 wiring is faulty. Partial loss of connection. Could be connector or fracture in wiring inside insulation.
-ECM C10 wiring is missing insulation and contacts with other wire. That other wire can't bee ground.
-CTS is faulty. However, I can't see why reverse gear would have anything to do with this.

If you have auto trans, issue that disappears when selecting reverse gear would make sense for two first reasons. Engine and wiring will move a bit.
Back up lights switch is on positive side of lamps. I can't be reason for CTS high voltage unless back up lights have lost their ground. Please check that back up lights are working normally, so we can exclude this for sure.

It may be hard to find faults on wiring. I had disconnection in wiring between distrubutor and ignition module. It could not be seen by eye, but by bending and stretching wire. However, fault is most likely near connection.
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yellowstone
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Report this Post10-25-2013 07:25 PM Click Here to See the Profile for yellowstoneSend a Private Message to yellowstoneEdit/Delete MessageReply w/QuoteDirect Link to This Post
I replaced the coolant temp sensor and pigtail and oil pressure switch today. My oil pressure gauge shows normal again and after a 10 minute test drive, the car behaved normally, no high idle episodes. I will do another, longer, drive tomorrow.

I also got TunerPro to work (finally) with a new cable and I have more data now.

The only thing I noticed when I looked at today's log file (and I've had this issue for a while) is that the battery voltage shows 13.3V throughout the drive but drops to 9-10V after I shut the engine off and I can't start the car immediately afterwards (it will hardly turn over). If I wait a few minutes, it will start again... any ideas about that one?
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fieroguru
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Report this Post10-25-2013 07:48 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by yellowstone:

after I shut the engine off and I can't start the car immediately afterwards (it will hardly turn over). If I wait a few minutes, it will start again... any ideas about that one?


Starter could be getting heat soaked, could be a poor wiring connection, or engine could have too much ignition timing (base timing setting).
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yellowstone
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Report this Post10-26-2013 03:46 PM Click Here to See the Profile for yellowstoneSend a Private Message to yellowstoneEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have done another 25 minute test run today and logged it with TunerPro, most of the time on the freeway.

Battery voltage is between 12 and 14.1V all the time:



That doesn't look like a problem with the alternator to me. The problem just occurs when I shut the engine off and try to start immediately or within a few minutes. Battery voltage will then be at or below 10V and the engine will barely crank over. The battery is new and was tested.

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Report this Post10-27-2013 05:54 AM Click Here to See the Profile for PhirewireClick Here to Email PhirewireSend a Private Message to PhirewireEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by yellowstone:

I have done another 25 minute test run today and logged it with TunerPro, most of the time on the freeway.

Battery voltage is between 12 and 14.1V all the time:



That doesn't look like a problem with the alternator to me. The problem just occurs when I shut the engine off and try to start immediately or within a few minutes. Battery voltage will then be at or below 10V and the engine will barely crank over. The battery is new and was tested.


on a semi-related note, I am having this occur to. But with my stock v6. I'd be fine driving, just on random occasions the battery would go below 10volts. even if its an hour later or a minute later.

Stupid question but are the battery terminals clean and tight?
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yellowstone
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Report this Post10-28-2013 07:35 PM Click Here to See the Profile for yellowstoneSend a Private Message to yellowstoneEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Phirewire:


on a semi-related note, I am having this occur to. But with my stock v6. I'd be fine driving, just on random occasions the battery would go below 10volts. even if its an hour later or a minute later.

Stupid question but are the battery terminals clean and tight?


But for me it doesn't happen randomly, just right after shutting the engine down. Yes, the battery terminals are fine.

I can't imagine what could possibly cause this...
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yellowstone
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Report this Post11-07-2013 09:41 AM Click Here to See the Profile for yellowstoneSend a Private Message to yellowstoneEdit/Delete MessageReply w/QuoteDirect Link to This Post
Finally found my multimeter! After the car sat for a few days, battery voltage was 12.27V. When I start it up, voltage is at 14.5V and even with AC and headlights on, it doesn't dip below 13V with the engine running. After I shut the engine off after a 20 minute drive the battery still shows 12.78V. However, when I then try to start it up, the voltage will dip down to 8-9V while cranking and sometimes the starter will make a tick-tick-tick sound. When I keep on cranking it over, the engine will sometimes start up and sometimes it will just seem to lose more and more battery power with the dome lights dimming and the engine not cranking at all.

Battery power when not cranking seems to be OK and voltage with the engine running seems to be OK, as well. The problem appears while starting and is more pronounced within a short period after I have driven the car.

Any theories based on this behavior?
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KY87fierogt
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Report this Post11-07-2013 10:58 AM Click Here to See the Profile for KY87fierogtClick Here to Email KY87fierogtSend a Private Message to KY87fierogtEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by yellowstone:


Any theories based on this behavior?


Do you have a way of measuring amperage draw? I am not an expert, however I did stay at a holiday inn express last night......
I suspect a bad starter/solenoid/wiring. Drawing too many amps when it becomes warm. If you could measure the amperage draw while starting cold and hot then compare the values.... Just my $0.02

Hope you figure it out!

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Report this Post11-08-2013 08:20 AM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
Sounds like a bad starter or starter wiring to me too. When you engage the starter hot, looks like it sucking up battery power.
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Report this Post11-10-2013 08:01 PM Click Here to See the Profile for darcfyreSend a Private Message to darcfyreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Had a 74 Opal Manta 28 years ago that had the same symptoms. Added a direct ground from the starter to the battery and it stopped. Went through and reworked all the ground straps and never had that issue again. Symptoms can have many different origins, don't give up, try everything.:-D
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yellowstone
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Report this Post12-11-2013 02:42 PM Click Here to See the Profile for yellowstoneSend a Private Message to yellowstoneEdit/Delete MessageReply w/QuoteDirect Link to This Post
I finally replaced the starter with a smaller and more powerful AC Delco unit (from a Grand Prix GTP) and that solved the issue. Starts and runs perfectly every time now!
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