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Help Chasing Erratic Idle Please

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Old 08-17-2017, 03:30 PM
  #11
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scan tool really is needed and would like to know how the past owner knew the IAC was bad. These IAC are the GM style that do not go out like what ecm 555 and pcm 555 uses. Yes they do fail these GM IAC but its like 2 out of 10 compared to 555's in which is 9.5 out of 10 for failures

Volvo Penta very currently still used that GM IAC and I rarely see it fail.

Last edited by BUP; 08-17-2017 at 04:09 PM.
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Old 08-18-2017, 06:22 AM
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Originally Posted by BUP View Post
scan tool really is needed and would like to know how the past owner knew the IAC was bad. These IAC are the GM style that do not go out like what ecm 555 and pcm 555 uses. Yes they do fail these GM IAC but its like 2 out of 10 compared to 555's in which is 9.5 out of 10 for failures

Volvo Penta very currently still used that GM IAC and I rarely see it fail.
I'm trying with all my might to get it scanned, you wouldn't believe the run around I've gotten from the shops. Latest was last weekend when I was told to call at 9 AM Saturday, no answer until 1 PM then I was told he was working on an emergency trailer job, call back Sunday at 1 PM. Called every 15 mins. From 1PM until 3 PM Sunday and kept getting the answering machine. That doesn't even count the months leading up which I was trying to get it scanned for hours and rpm log. .......and that's my best lead on getting it scanned.

The mechanic doing the pre-purchase survey told me. As described in post #1 it came out in pieces. I can hear it whistling when trying to keep it running on the hose so I doubt it is the culprit this time.

Keith

Last edited by Tractionless; 08-18-2017 at 06:25 AM.
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Old 08-21-2017, 11:53 AM
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I used CRC 656 and a toothbrush to clean the small harness side connectors. The ECM harness was pristine.

Today I tested the ECT for 5v, it's good. I replaced the ECT for good measure as well. For $17 it's not worth testing the temp. range on a stove top.

I tested the TPS harness side per the manual as well and when I got to "hook a test light to battery + and then touch the light to blue wire on the harness side connector, does it light?" it did not light and flow chart says replace TPS. Again for $39 w/lifetime warranty I'm in the middle of replacing it as well.

During the key on procedures above I can hear the IAC whirring away for a couple of seconds. At least it sounds like it's still in on piece. IAT harness tests good as well and I cleaned the sensor with MAF cleaner.

After 10 hrs. Installing new trim tab hoses and locator system and doing the above didn't have time to start the engine to see what if any change I made.

After setting the new TPS to 0.7V at idle last night the engine idles (cold) on the hose at the correct rpm and without any issue. The real test will be after being out on the water then flushing to see if it will stay running or not. Hopefully this weekend if the weather holds up.

Keith

Last edited by Tractionless; 08-23-2017 at 07:30 AM.
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Old 08-31-2017, 07:35 AM
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Following up wih the last paragraph of the above post.

Fail on idle again at the ramp. Fired it up and it was pouring out black smoke and idling at 1100 rpm. This is after running perfectly on the hose last week, no changes were made. I checked the new tps and it was at 0.7v as tested above. Swapped MAP sensors and it was no better. Code reader got "TPS high" and "coolant temp. Low" and would not clear them. I tried adjusting the TPS value down and it wouldn't net below 0.6v at idle, put the old TPS back in and set to 0.58v (lowest it would adjust) which netted clean burning exhaust and 600 rpm idle. Codes still read "tps high" and "coolant temp low" Took the boat out and around 1k rpm it still surges (TPS value stays steady) . Put it back on the hose to flush out (at the ramp) and idle was steady at 600 rpm.

Short of trying another IAC (current has less than 20 hrs on it) or swapping ECU's I'm out if ideas.

As stated by others above the scan is desperately needed while on the water and the issues are present to see what is happening with all sensors etc. at the same time. I guess I'm not going to solve this on on my own.

Last edited by Tractionless; 09-01-2017 at 06:48 AM.
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Old 08-31-2017, 08:21 AM
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Suggest checking connections to IAT, MAP, ECT and TPS and note the common ones
Attached Thumbnails Help Chasing Erratic Idle Please-grounds.jpg  

Last edited by AllDodge; 08-31-2017 at 08:34 AM.
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Old 09-01-2017, 06:46 AM
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Originally Posted by AllDodge View Post
Suggest checking connections to IAT, MAP, ECT and TPS and note the common ones
Checking as in with a multi-tester as per the manual (non-scan) approach? I've done all but the MAP and they were fine. Will check MAP next. Thanks
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Old 09-01-2017, 07:00 AM
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Check all your grounds after that.And clean them all even if they look good.
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Old 09-01-2017, 07:10 AM
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One more thing.I have seen iac sticking after just a short time.

If the old one was sticking and you still have it I have cleaned them and then used teflon lube in one's on other vehicles and it lasted many years.Remlube is what we had at the time.

Never tried it on a merc one thats why i suggest the old one.

Just an idea for a cost effective fix.
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Old 09-01-2017, 07:13 AM
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Oops just saw the old came out in pieces.
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Old 09-20-2017, 01:45 PM
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Originally Posted by Warship2k15 View Post
One more thing.I have seen iac sticking after just a short time.

If the old one was sticking and you still have it I have cleaned them and then used teflon lube in one's on other vehicles and it lasted many years.Remlube is what we had at the time.

Never tried it on a merc one thats why i suggest the old one.

Just an idea for a cost effective fix.
Been on a small hiatus since being affected by Hurricane Irma but getting back into working on this issue.

Where do I apply dry teflon lube? Shaft that screws in and out? I have a new IAC coming (I'll lube that on too) and while having the TB off I'll wokr on getting the TPS more closely adjusted to 0.48 as advised.

I spoke with MEFI Tuning who suggested making sure the TB fully closes which I'll do but highly doubt it's the issue with 268 hrs. Then they advised to swap ecu's between engines.

Keith
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