Need some helps, thought it was EGR
 

Hey Gang-

Happy Holidays!!

I need some help if you would- I've searched several forums and found no real direction, so I apologize if I missed it...

The patient:

92 SC400 139k miles, maintained well - California Emissions equipped car,

Stock everything.

When I bought the car, we thought it had a faulty EGR Valve - was throwing a code 71, I still bought it, it was a good negotiating point and plus, I have a '93 California Emissions SC400 that is running fine, will be a project down the road - I drove it everyday until I stumbled across the patient here.

Anyway, so here is what the car is doing-

Start it, it runs for a second and then dies - start again and it stumbles and with 50% throttle coughs sputters as if the ratios are off and then after you get it revved a bit above say, 2k - it clears and runs somewhat ok with a cough now and again.

So, I switch out the EGR Valve with the other car, new gasket all good and start it, it's worse. This is after clearing the codes with pulling the EFI fuse by the way. Cleaned out the passages as well also.

Put the defective EGR in the other SC and it starts up without an issue, runs great.

So much for the faulty EGR.

Other Info -

Car is cold - and if you unplug the EGR it runs fine - Drive it all day that way, Check engine light glows - but that is obvious.

Possible IAC?

I appreciate the help guys, I have the next few days off and would love to address it-

Have a great day and sorry about the long read there-

~Brian

Leaning towards IAC
 

Hey there again,

If anyone knows of a thread that they've experienced this same issue, let me know and happy to review - all the ones that I read seem to dead end with no continuance to the solution-

thanks again!

I may be speculating, but could this possibly be an ECU issue? Hopefully someone else could chime in.

I thought about that, but it seems strange that it runs great with the EGR unplugged - it's like once I plug the EGR in it is completing the "circut" to whatever is the culprit...

My suggestion would be to switch the ECU from the good running SC4 to see if that works.

Well, I happen to have the other SC400 to do that with - it's a '93 but still a California emission car so they share the same part number so that is good...

Can someone chime it as to why the ECU would come into play only when the EGR is plugged in?

Seems that it would show other signs of ailing even with the EGR unplugged-

I plan to try it, just trying to understand how they relate so I can get my mind around it...

Just because the EGR valve is not faulty doesn't mean it's operating correctly--the ECU controls its operation. If the ECU has failed such that it is commanding the EGR valve full open when it shouldn't be, that could cause the issues you are experiencing. Obviously, by unplugging the EGR, you are preventing it from opening (even though the computer is still trying to open it), thus, eliminating the problem.

My guess would be the fuel pump ECU is going out.

Give the 12v Fuel Mod a shot: https://www.clublexus.com/forums/per...tures-faq.html

75% of SC issues usually round up to being one of the 2 ECU's that went or is going bad. When something works better when unplugged, it's bound to be ECU something. Try the 12v mod like Kira added, and if that doesnt do it, pull the ECU out and have a look at the capacitors. Check for leaking or corrosion.

you could just be going into limp mode with the check engine light on when you unplug it thus it appears to run "better". sort of like when you disconnect the maf and it seems to run better. you could have had another closed loop issue arise inbetween reset's which is why it seemed to run worse when you reset it the memory of the correct values are gone now, its possible the egr code could be a byproduct of some other problem like the ecu. when you have the egr disconnected and try and unplug the maf and see if its different or the same. if its the same its a closed loop problem and could also very well be the ecu, worth a quick inspection inside for leaky caps if that is the case.

its possible to be a wiring problem, maybe check the drivers side tire well there is a harness above the plastics when previous owners drop the car sometimes they can rub through a few wires but I don't think that is the case, but worth a quick check.

Update
 

Hey Guys-

Thanks for the posts, I appreciate it-

Ok, I finally had a chance to address this a bit, this morning it was really cold and it gave me th,e most issues to date. It would start, run, then die. Then it eventually would idle but if you gave it throttle, would die. After getting it to rev a bit it acted like it wanted to run but when I drove it, it wouldn't respond to throttle at all hardly and I barely got it back up the hill to the driveway.

After shutting it off, restarted it and it ran great - has run all day without a hitch - this by the way was with the EGR unplugged from the get-go.

So, I got home - left the EGR unplugged and did what Ali suggested and unplugged the MAF and there was no change - car started up just fine and ran great.

I am going pull the codes here shortly but am open to suggestions -

By the way, this is a calif emissions car so the VSV is only there for the evap, and there is no egr vacuum modulator that I can find....

thanks!!

Quick question also -

If I take the ECU out of the '93 that is also a Calif car with the same part number - will this identify if the ECU is problematic or is there a "learning curve" for the ECU since it's a different car?

man just swap the ECUs and stop procrastinating its FREE why are you making it harder than what it is? disconnect your batterys on both cars swap the ecus and see what happens

This. When my fuel pump ecu was on its way out it manifested in the form of the car dying when I used the turn signals...