bernie.lomax

Hi, hoping that the maxima community can help me diagnose a problem. I need help & thought I would try. Here goes:

2000 maxima se, manual w/ 130k miles & a CAI mod, otherwise all stock, car was running fine prior to the IACV acting up (faster idle than normal, then pulsating idle around 1500-1600, then idle around 400 which would snuff out unless engine fully heated up)...problem emerged on a Tues. night & I had to continue driving car until Thurs afternoon, so at least 1 day of driving car while IACV was faulty (total drive time approx. 3-4 hours)

I took off the TB & replaced the IACV with a new hitachi unit (new unit showed 22.8 ohms resistance on the tested tabs); old unit showed ohm resistance numbers of 1, 1.8, etc. so old unit was definitely defective

The TPS grey connector with the green tab would not release from the TPS body, so removed the TPS unit from the TB with grey connector still attached. Re-attached the TPS to the TB in what I believe is same position as it came off at. Re-attached all connections/hoses/cables & fired up the engine.

Seemed to work fine & after warm up, idle resumed to approx. 800, so I was satisfied, although idle does seem a tad high. Did not perform the idle air volume re-learn exercise, as engine appeared to be running fine without it.

Drove the car & discovered that with the accelerator depressed at approx. 1600-1700 rpm engine speed & again at approx. 2100-2200 rpm the engine runs really rough. Engine might even be cutting out, bogging or stalling momentarily & then due to inertia/momentum carrying it past this "dead zone", the engine runs fine at rpms either above or below the 2 "dead zones". If I try to maintain engine rpm at say 1600-1700, the engine continues to run really rough & car bucks back & forth like it is sputtering or like I am jabbing/releasing/jabbing/releasing the accelerator. If parked in driveway in neutral & try to keep engine rpm at 1700, the engine speed fluctuates up & down like I am revving the engine, however, my accelerator pedal position does not change. It does not do this all the time, so it is intermittent & does not throw a code. Appears to not do this when the engine is cold, only after it has been running for 5 mins or more. Does not appear to do this in 2nd or 3rd gear, etc. Dead zones only present in neutral or 1st gear.

Have so far only noticed the problem when accelerator engaged & engine rpms are going up (nothing detected when rpm speed is decreasing through the "dead zones").

I live in toronto canada, so it is winter condition, & problem is noted in 0c (32F) or -15c (5F) ambient weather conditions.

I thought that perhaps the TPS was to blame & wiggled the 2 connectors & slightly adjusted the TPS setting by rotating the body slightly after loosening the screws. Drove car & there was no change in the problem. Thinking of adjusting the TPS body setting a bit more, however, I am not sure that it is the cause. I will perform the idle re-learn for a 5th gen to see if that changes anything.

I read that a faulty IACV can trigger problems with the ECU. Does what I have described sound like a faulty ECU? Does the problem sound like something that could have been caused by the IACV damaging/affecting the ECU?

In your opinion, what do you think is happening? I am able to take trouble shooting a fair distance, however, will need to kick it over to a pro (possibly stealership for Consult II diagnostic) if it gets beyond my ability. Car is driveable, however, a real nuisance & do not even think of drinking hot coffee, otherwise will have it spilt all over if engine acts up while drinking.

maxiiiboy

I am afraid that your suspicion is correct. However, the only way to find out is to visually inspect the ECU. Don't panic and read this document first: https://drive.google.com/file/d/0B6O...1fNlF5QjQ/view . Then, visit this thread https://maxima.org/forums/5th-genera...d-seconds.html to see how a damaged ECU, and a damaged STA509 transistor in particular, looks like.

My car (2000 SE with 133.8K miles) seems to be very similar to yours. I expect it to run for at least another 5 yrs. So, don't get down on yourself and get it fixed - my note has multiple references on how to fix a damaged ECU.

bernie.lomax

hi, thanks very much for the reply. Read the ecu fried thread & was not able to pull up the photo showing the blown STA509A chip & the burnt circuit board. If you have a pic or a source you could refer, much appreciated.

Read your manual & it is very informative. Trying to confirm if the symptoms I describe would indeed fit the pattern for a blown STA509A chip. If is seems like a blown chip or partially blown chip would cause my issues, then would replacing just the chip (provided nothing around it is burnt/damaged) allow the ecu to function properly again?

I am trying to pose the same question to one of the ecu repair shops that you sourced out in your manual. I am not able to pull the ecu out to visually inspect until the spring or 3 months from now.

Would I be running the risk of further damage to the ecu or the engine if I continued to drive for a few months? I am assuming that any collateral damage to the new IACV would have already occurred by now.

your thoughts/time is appreciated

maxiiiboy

This is how a damaged ECU with a burnt STA509 looks like:
http://i39.tinypic.com/xofndu.jpg
https://maxima.org/forums/attachment...814_190352.jpg
And yes, replacing the STA509A chip should fix your ECU. Many .org members have done it.

Re. further damage, it's hard to say. It's certainly possible.

bernie.lomax

thanks very much for all the info & help...I will need to pull the ecu & look inside & hopefully it is just the STA509A IC that is damaged...if I were to replace the IC, do you know if there is any re-flashing or calibrating of the ecu required? (assuming no other components were damaged when the IC cooked)

do you know if a dealership consult II diagnostic would detect the blown STA509A IC? or any other damaged components? or is hands down best way to visually inspect?

will now research on tips on how to remove the ecu...car is my daily driver, so cannot be without for more than a day

thank you again

bernie.lomax

hi, trying the community again...you all have been very helpful & I was going to go to the "well" one more time...as suggested, I pulled the ecu & inspected it...circuitboard showed no evidence of damage...the location where the STA509A chip is on other circuitboards had a 15 pin chip (8 pins & 7 pins on other side) & there are 2 of that style chip...did see a pair of STA508A chips located elsewhere on the board...took photos, however, do not know how to post pix

2 questions; is ecu pin 6 the sixth pin from the left for the second cluster of pins from the left? (the first cluster in the left corner of ecu contains 8 pins)...does pin numbering complete a row & then starts again on next row to the left (ie. pins 1-10 on top row, pins 11-19 on second row, etc?) I noticed some carbon deposit on sixth pin from left on top row of pins...I believe this is the pin for the circuit which usually blows the STA509A

I also noticed green corrosion build up on the 7th pin from the left in the second row of pins (pin 17 from above numbering system)...in the 4th & bottom row of pins, the 3rd pin from the left had some dirt (maybe carbon, not sure) on it...cleaned all pins & took photos before they were cleaned...cleaning did not help; symptom is still there

2nd question; do you know if the dealership consult II diagnostic is specific enough to diagnose exactly what components/chips have failed within the ecu? this problem is occurring & is not throwing a code, so is it occurring undetected by ecu?

any thoughts are appreciated...thx

maxiiiboy

For posting: your Google drive, or Photobucket, or other. Then post link.

Derrick2k2SE

iTrader: (3)

Now you can hit the picture icon and select a pic right from your computer or device. Just click the icon, click "browse device" and go from there. I don't know when they changed it, I think some time last year, but it works really well.

bernie.lomax

ok, I will try to post...these should be pix of the circuit board...will post pix of pins in second batch

hopefully this link works

https://onedrive.live.com/redir?resi...nt=photo%2cjpg

bernie.lomax

ok, think I got the link to work...here it is, please let me know what you think...please select the Go To Onedrive & view email attachments

https://onedrive.live.com/redir?resi...nt=photo%2cjpg

here is the commentary which goes with the photos...thanks in advance

trying the community again...you all have been very helpful & I was going to go to the "well" one more time...as suggested, I pulled the ecu & inspected it...circuitboard showed no evidence of damage...the location where the STA509A chip is on other circuitboards had a 15 pin chip (8 pins & 7 pins on other side) & there are 2 of that style chip...did see a pair of STA508A chips located elsewhere on the board...took photos, however, do not know how to post pix

2 questions; is ecu pin 6 the sixth pin from the left for the second cluster of pins from the left? (the first cluster in the left corner of ecu contains 8 pins)...does pin numbering complete a row & then starts again on next row to the left (ie. pins 1-10 on top row, pins 11-19 on second row, etc?) I noticed some carbon deposit on sixth pin from left on top row of pins...I believe this is the pin for the circuit which usually blows the STA509A

I also noticed green corrosion build up on the 7th pin from the left in the second row of pins (pin 17 from above numbering system)...in the 4th & bottom row of pins, the 3rd pin from the left had some dirt (maybe carbon, not sure) on it...cleaned all pins & took photos before they were cleaned...cleaning did not help; symptom is still there

2nd question; do you know if the dealership consult II diagnostic is specific enough to diagnose exactly what components/chips have failed within the ecu? this problem is occurring & is not throwing a code, so is it occurring undetected by ecu?

any thoughts are appreciated...thx

bernie.lomax

bumping this thread to get the newly added link noticed...commentary is one post above

https://onedrive.live.com/redir?resi...nt=photo%2cjpg

maxiiiboy

Your link does not work (I get a "This item might not exist or is no longer available" message). However, there is a better way of posting, directly on our server: just use the "picture" icon (5th from the right, just above the composition window where you compose your message).

bernie.lomax

ok, I think I finally got the pix uploaded...apologize for them being out of order...the last pin photo is taken with the ecu upside down...pls let me know what you think...symptons are described above...thanks in advance

maxiiiboy

Your ECU looks OK, at least from the distance. Here is a diagram of the ECU pinout (from another post on this forum):



Coloring: Red is power, black is Ground.

bernie.lomax

thanks for the ECU pinout diagram, based on its numbering:
Pin 6 had a slight carbon build up - could this be evidence of an electrical surge tied to a failed IACV?
Pin 17 had green corrosion
Pin 32 had slight dirt/carbon build up, discoloring the pin relative to the other pins


do any of these pin conditions tell you anything?


is it possible that there is still internal damage to the IC chip that cannot be seen from the outside? Is it likely?


again, any assistance is appreciated

manilakid3

A damaged ECM doesn't have to look like the one you posted. My STA509 chip was blown but visually it wasn't that bad.

When I opened up the ECM for the first time, it had a very bad burnt smell so I knew something was wrong. Also, there was a brown spot on the metal bracket right on top of where the burnt chip is located.

Any damage to the STA509 chip has to be changed. Got mine done for $90 + shipping from a company in So Cal. Getting it back hopefully at the end of the week.

maxiiiboy

You paid a lot. You can get them on e-Bay for about $10: http://www.ebay.com/itm/STA509A-Sank...0AAOSwqv9V6I8B

cornholio

iTrader: (1)

i think he's saying he sent his ecu off to be repaired for $90, which i believe is on the cheaper end of what i've seen.

manilakid3

Yes you are correct.

maxiiiboy

My fault. Yes, $90 for having it done is a great deal.

bernie.lomax

from the condition of the circuitboard & the chip, do you think there is any damage to ecu? or hard to tell/ could be hidden /internal in a chip

do the condition of the pins look like they are an indicator of internal damage to ecu?

trying to determine if the ecu is still semi-fried based on throttle flat spot problem that engine has

any help is appreciated

btw, are you guys familiar with the chips on my circuitboard where the STA509A is supposed to be?

manilakid3

The STA509A is written on the chip.

Turn it over and check the other side if you see any burnt parts.

Also, when you opened up the ECM, was there a burnt smell?

Did you also check if an obdii scanner can read your ecm?

bernie.lomax

there was no burnt smell in ecu

the chips in my ecu are not the STA509A type

checked with dealership, the Consult II reader is not specific enough to read a problem with a component inside the ecu...it just reads the codes that the ecu throws

do you have the name/contact info for the place in so cal that is rebuilding your ecu?

also does anyone know if the cheap china built IACV units on ebay work / are worth a gamble? the hitachi built units are much more expensive

manilakid3

I just replied back to your pm. But it seems like your ECM might have been spared. You might not have to get it fixed. A clear indication would have been a burnt smell when you opened the ECM for the first time. Its up to you if you want to send it in anyway.

bernie.lomax

Trying the community again on this problem which is still the same from the first thread. Engine only acts up when at normal operating temperature (no issue if engine is cold or not warmed up) & only causes the "bucking or hunting" in 1st gear or parked in neutral.

Parts I have swapped in or replaced to troubleshoot are:
ECU (replaced)
Engine temperature sensor (replaced)
TPS (replaced)
MAF (disconnected it & the engine speed "hunting" still occurred at 1800 rpm & 2200 rpm)
AICV (replaced)

I currently shift out of 1st gear just before hitting the 1800rpm soft spot & then while in 2nd gear it revs smoothly thru the 1800rpm soft spot (same applies for 3rd & 4th & 5th gears). So my driving style avoids the troublesome rpm. If I forget to shift & hit the 1800rpm in 1st, car will buck, like mentioned in the initial post.

Could it be crank position sensor or cam position sensor?

Any informed suggestions would be welcome, cuz I really do not know what is causing this annoying problem. Otherwise car drives fine. Thanks in advance.

bernie.lomax

Hi, checking in with the community to see if anyone has some suggestions/advice on how to fix the problem outlined at the bottom of the thread...appreciate your time

5thgendriver

from what I have read you have to replace the edu and the iacv at the same exact time. did you do this?

bernie.lomax

thx for reply...I believe the IACV malfunctioning can short out components in the ECU, so some recommend replacing both at same time...however, upon inspection of my ECU (pix are uploaded in the thread) there is no evidence of the ECU circuitry being affected; no burnt smell or visible burnt/fried components...so both the ECU & the IACV were replaced separately

if there are any other suggestions/thoughts/experiences on what kind on "gremlin" this is, I am all ears

Dj*Bogus*31

Hey Bernie lomax.....did you ever find a solution? What type of iacv did you use? Hitachi or did you go with the cheaper brand?