Hard start/Funny idle - 7mgte ISC problem?

[Alang]

Hard start/Funny idle - 7mgte ISC problem?

Is this an ISC problem? Maybe it isn't closing fully? or??
Any other ideas? Where do I start looking?

Out of nowhere, my 7mgte began to start funny. I would have to work the throttle to get it to start and then continue to work the pedal to keep it running at 2k rpm or so. It would be running rough with the vacuum gauge needle fluttering hard at 5, when normal idle is 17-18 without flutter. It would run this way for about 1-2 minutes and then suddenly it would smooth out and give normal vacuum reading. Cold starts or warm, this went on for about 10 days and then it seemed to go away. What remains though, is a starting idle that often has a bit of a lope or roughness to it for a short period. The MPG has dropped from 18+ mpg to barely 16 mpg, My codes are unchanged (32,42,51,52) that have been in place forever. Light load shows a reduced vac reading dropping from 10 to 5ish. The cold idle vac reading seems down by 1-2 points.

 

[Alang]

Typo?? think you mean code 52

"Code 51 is the knock sensors...usually a wiring issue. With that code present, the ECU retards timing quite a bit and the car runs like crap."


The TSRM says 32 is the AFM. What is the HAC sensor?

"Code 32 is the HAC sensor...it in the ECU on '89+ cars...separate sensor next to the ECU on '87-'88 cars. Of these codes, this has the least impact unless you live at higher altitudes (like Las Vegas). Generally the engine will run rich with this code."

No. It idles OK. The idle problem just occurred for 10 days and then mostly resolved. Wouldn't a vacuum leak have a larger impact on the gauge reading?

"You really, really need to get these fixed. It's no wonder it doesn't idle worth a crap...sounds like you have a vac leak too. "

 

[Alang]

The cynus TSRM shows 32 w/asterisk referring to the 7mge

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=27

but where does it link the 32 to the HAC sensor which is shown as a 35 w/asterisk referring to 7mgte?
And what is the HAC sensor?

 

[92TealSupra]

The cynus TSRM shows 32 w/asterisk referring to the 7mge

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=27

but where does it link the 32 to the HAC sensor which is shown as a 35 w/asterisk referring to 7mgte?
And what is the HAC sensor?

I find it weird you trying to correct him on most things here, but the last time I checked ( I JUST READ THE WHOLE THREAD ) you're the one trying to fix a problem and he knows what he's talking about, if I were you I would re evaluate everything before you start correcting people that are indeed trying to help you, but it seems like you know everything, I guess you can close this thread now.

 

[Alang]

The HAC is a high altitude compensation sensor that is a separate from 87-88 ECUs but integrated on 89 and later. It apparently modifies the injection for the altitude.
see the good writeup inside this pdf.
http://www.autoshop101.com/forms/h24.pdf
It doesn't describe what the full path from an engine location to the ECU is.

 

[jetjock]

So many "experts" and so little time eh Dub? It's why I'm posting less as time goes on.

My codes are unchanged (32,42,51,52) that have been in place forever.

Your plea deserves to be blown off on that alone...

 

[Alang]

Got a HAC Sensor, installed it and makes a very noticeable difference. Immediately got 1-2 inches of vacuum at idle and light throttle cruising as well as sharper throttle response.

How did the confusion come about? Strange change in Diagnostic Codes?
The swap was done by a very knowledgeable Supra wrench who failed to swap in the HAC sensor from the donor car. Another thing is that my usual reference point is the online Cygnus TSRM which is for a 90 gte. It shows Code 32 as the AFM and 35 as the HAC sensor. During SILV last month, Dave Shepherd gave things a looksee and explained the distinction between 86-88 and 89up wiring. He also identified that my ISC is probably stuck and is not resetting. I found an 87 TSRM online that shows the variation in code 32 between the GE and GTE models.
This HAC sensor code change early/late model is sort of a weird change in codes. It seems odd that the HAC code changed from 32 to 35, but it likely has to do with the incorporation of the HAC inside the ECU on the later models. Curiously, 3 or 4 generally familiar guys that I asked were unaware of the distinction.

After a reset, my codes are gone except the 51.
What does the ECU adjust with a code 51?
If my TPS reads OK, then I should look at the neutral start switch?
(Mine sometimes fumbles when the car is parked uphill)

 

[Alang]

Further Update
Installed a HAC sensor (pre 89 harness). Car has had no HAC sensor since the 7mgte conversion. Put one in and instantly got 1-2 points of vacuum at idle and cruising. I also went from 4.10 rear to 3.73. No other changes, adjustments, or maintenance. Seems closer to what the car should be. Still can't turn more than 5 lbs boost.

Another LV-LA Road trip MPG report:
outbound 3200 rpm 90 MPH cruise 23.1 mpg
return 2500 rpm 72 MPH cruise 24.2
No A/C operation

Next Local 200 mile operation 19.8 MPG

Much satisfiying improvement. The next thing to check is the ISC and CSI. There have been some small operating variances that suggest that they should be cleaned and checked. Will also be doing a Manual boost controller to check on the limited boost.