I've been attempting to troubleshoot a high idle problem. I connected a new scanner from Auto XRay to my 85. I'm not sure what to make of the results. Here's what the scanner is telling me at idle and normal operating temperature.

IAC Counts = 60
TPS = 5.4v
MAF = 9 grains
MAT = 203 deg
EGR = Off
Coolant temp and RPM are very close to what I see on dash gauges.

Is it normal for the engine to idle higher with the scanner connected? When I shut the engine off, MAF shows 5 grains. Shouldn't it be zero?

 

I have the A X ray 5000, and I realy llike it. I believe there some settings that change when your hooked up to a scanner. Cant remember the changes right now. Its been awhile.

Corvette Mike

 

Your Idle should not change when connected to the scanner.How high is your car idling? Here are a few thoughts I had. First check and make sure there are no cracks in your air duct after the maf, be sure to check the undrside real good.With your scan tool connected watch the Iac counts,Rev the engine, does the iac move (on the scanner)? If so I would remove the Iac and clean it of all carbon. I have seen them hang open from a carbon chunk. dont forget the seat where the needle rests.Does your ECU have long term fuel trim? Ltft. If so what are the values?Lastly look for any other vacuume leaks. Intake gaskets, small hoses brake booster hose etc..

 

Verify that the TPS is .54 volts, though if it were 5.4 volts, there would be trouble code and running on backup. 60 counts is being commanded for a reason - Need Coolant Temp Sensor Signal; A/C request; Targeted Idle and Actual Idle; Load Variable; Park/Neutral or Gear Signal OR post all the Data, not just a few items.

The MAF senses the air around it - even with the key off - so a reading with it not running is normal.

 

#1 Call Auto Xray and find out if your scanner with work with the 85. Mine will not. I was told by them that the scanner does not support the 85 computer chip. There is NOTHING in their directions that come with the scanner that will tell you this. I tried to use it to run down codes in the computer. The scanner would give me a odd ball code that was not related to the problem. I now use the paper clip method to pull codes.

 

I typed the TPS value a decimal off. I will rerun and record all the values. Thanks in advance for any help here.

 

I own a 6000 series tool and it would not work on my 93, lots of calls, e-mails, and exchange of 3 scanners finally delivered one that would function as advertised.
Do not settle for a tool that will not perform as AutoXray indicated, if they say it will not work on your vehicle ask for a refund and be persistent.

 

When I hook my Auto X Ray 6000 up to my 89 the idle does go up slightly. Hook the scanner up, get the car up to operating temp, then take a reading. You should have the book to tell you which readings are within spec and which aren't. If you have a Factory Service Manual that should tell you what the readings should be and help you find the problem if the readings are out of spec. Having someone else drive the car while you actually view the live data is the best way I have found to see whats really going on, this is how I found out my EGR wasn't working properly.I also found that my (block learn) wasn't at 128 which is a neutral reading when there is no fuel or air compensation being made, this indicated a problem with my O2 sensor. ...WW

 

I reran the scan with the engine at operating temperature and captured the data.

Idle Air Mtr Pos: 47 Steps
Coolant Temp: 167.9 deg F
Vehicle Speed: 0 MPH
EGR Duty Cycle: 0.0%
Engine RPM: 1000
Throttle Sensor: 0.56 Volts
Integrator: 124
Oxygen Sensor: 836 mVolts
Manifold Air Temp: 203.0 Deg F
Knock Sensor: 112
Block Learn: 179
O2 Cross Counts: 0
Mass Air Flow: 8 Gr/Sec
Injector Pulse: 1.3 mS
Learn Control: Enabled
Rich/Lean Flag: Rich
Loop Status: Open
Park/Neutral: Detected
Power Steering PSI High: No
EGR: Off
Fan #1: Off
A/C: Requested
Prom ID: 7805

I noted a few things.

Manifold Air Temp never changed. It read 203.0 at startup with engine cold. Scanner indicated A/C was requested. The A/C was off. Computer never went to closed loop. Chip is programmed for 800 RPM idle target. Actual idle was 1000. Idle increased when scanner was in scan mode.

 

knock sensor - 112 being one thing you need to look into and secondly your iac counts are high.. try cleaning your tb. try unplugging your MAT sensor to see if the value changes.. it should read like -55

 

In Open Loop some of what's showing is meaningless, but I'm beginning to think your setup (Scanner) isn't working. A BLM of 179 is off the Chart and it should show what it was the last time it was in closed Loop and shutdown. A/C Request should be a Yes/No and if it just says A/C request it isn't reading the signal. MAT and the Coolant Temp Signal should be the same or close and about ambient on a cold engine; ie, one that's sat overnight before it's started. Once started, it wouldn't be unusual for Intake Air to rise above Coolant Temp. Coolant Temp should rise to the thermostat and when it opens, drop a degree or two before rising to the threshold for Fan Operation. Either Sensor disconnected should read -38 degrees; grounding the signal wire should be 300 degrees. Actual Idle should be 100 rpms +/- Targeted in Park/Neutral; 50 rpms +/- from Targeted in Drive (If an Auto). I'd try the Stock Chip and rescan or maybe as suggested, the Auto Xray doesn't work with this Year. You might also disconnect the TPS with it running and see if generates a 22; verify the Check Engine Light.

 

Thanks for the reply. I have an email into Auto Xray to confirm this scanner works with my year but I'm guessing it is working. I'm pretty sure the MAT is shot. It indicates a 203 F temp with the engine cold. Coolant temp seems to track with the thermostat so I think its good. TPS seems to be functioning, although it may be tired. I found a broken wire to the EGR Temp Switch. That may be contributing to the idle problem. So now I need to pull the SR plenum to fix the EGR switch and MAT. Your idea to check with the stock chip is a good one. I'll try that.

How do I find out what each of the scanned values should be? The FSM doesn't help.

 

The scanned values change with engine operating conditions so there is no single correct answer. The ECM uses those inputs to determine spark advance, injector pulse width and so on.
Understand that the values displayed in your list are a snapshot, just one moment of engine operation.
I recommend purchase of Corvette Fuel Injection by Charles Probst, it will give a basic understanding of EFI and also provides reference for typical sensor values.

http://www.amazon.com/Corvette-Injec.../dp/0837608619

 

Thanks. I've been looking for a good book. This looks like the one.

 

I'd still verify the Check Engine Light and the ECM's ability to store/recognize a troublecode/problem. Here's why: The last time it went Closed Loop it was incredibly lean - probably so much so that it should have thrown a 44. That should have put it on backup and as long as the problem exists, the Check Engine Light should be staring you in the face and it won't switch to closed loop (and the main fan would be running - is it? That Coolant Temp is almost 25 degrees below the stock thermostat!). If this was an O2 problem it should have thrown a 13, but I'm guessing it's on backup and there's something preventing you from seeing that.

As to your idle, air flow is normal. The IAC counts could probably be 10 to 20 less (and they may be high because it's on backup), BUT, with the BLM being as high as it is, the ECM is dumping fuel to correct for the perceived lean condition and that extra fuel speeds it up. BLM's - when they're this lean - are usually due to a fault in the Air Pump system - either is continuing to pump air to the headers when it should be going to the CAT or a Check Valve is shot, or someone has put on aftermarket headers and they don't fit or seal to the head due to inferior build quality. Before you do any troubleshooting though, it's best to verify the ECM and Check Engine Light - it'll make it a lot easier.

 

I know the check engine light works. I have a cheap code reader that has verified I get Code 12. There are no other codes stored.

I'm finding I have multiple sensor problems. The Manifold Temp Sensor is reading 203 deg F with the engine cold and it never changes. That can have an effect on fuel mixture. I believe it would lean the mixture. Also, the EGR is not working. The EGR Temp Switch has a broken wire. The TPS appears to be sticking. Sometimes I get the correct idle, other times it stays high. The scanner showed it was not always going back to the throttle closed voltage. The coolant temp is displaying correctly. I have a 160 thermostat. The scanned temp is very close to the dash display. The engine does go closed loop but when idling it will sometimes go back to open. I've read that is normal.

So for now I have the sensors on order. Yesterday I got an excellent book on Corvette fuel injection. I just need to correct the known problems and see if it clears up some of the unknowns.

Thanks for the input. I'll post the results for anyone else that might have similar problems.

 

what is exactly modified in this car? Does it have an aftermarket tune ?
That blm is WAY OUT OF CONTROL, to the point of extrme lean condition and possibly hurting that motor. Regardles of 02 readings, and the int. of 124, it is nowhere close enough to be able to comp. The 02 number should be moving around and not be static at 800+, similarly the crosscounts should be moving as well.
It should not be able to go from closed to open loop while running once the parameters of closed loop have been attained....unless, the 02 has been moved to the collector and is not a heated 02.
do some reading here:
http://www.thirdgen.org/techboard/di...uide-book.html

 

As far as I know, MAT is only used for EGR operation.
Maybe if you compare TPS, IAC counts and spark advance, during low idle and high idle, it might help to understand why it's happening.

 

Thanks for your comments. Not sure what to do with them.

Modifications include a mild competition cam, AFR 195 heads, Super Ram, TPiS headers, Bosche III injectors, TPiS AFPR, Fastchip, 160 stat. Yes the O2 is near the collector. It is not heated. The reading does move around. What I posted was a snapshot. According to the book I got on Corvette fuel injection, the ECM can go from closed to open at idle. But it does go closed when driving. I may need a heated O2.

The engine does not seem to be running scary lean. I'm getting a nice coat of carbon in the pipes and the fumes do not burn my eyes. As I stated, I have some sensor issues to deal with. Once I correct the known problems, I'll deal with what is left.

 

After you have determined if there any mechanical/sensor issues you will need further scanning. While at idle you may see some carbon on the "tips" does not mean it isn't go lean at another rpm v.s. load range (and it is hence the 178 blm). You will need to then need to find what area (rpm vs load) is going that lean and this will need to be addressed in the tune. To accomplish this you will need more than a snap shot of what is going on (data log) and send it to your tuner so that specific areas can be adjusted.
While 1000 rpm @idle is a tad high, your higher than stock idle, it would be typical to bump up the idle for a modded car/tune. To understand were the idle was set at, you should have something titled "target rpm" for idle. Again, once all the parameters have been met (operating temp. for closed loop, timers etc.etc.) for closed loop operation, it should not be going back into open loop until it is shut off and re started.

*stupid server cut me of last night from finishing this post*