Hey everyone... This is my third post so far about my issue. Everyone has been great with helping me and I really appreciate all of your words, advice, and guidance.

Here is where I am. I have replaced just about everything you can think of, and having a major issue with how I'm running. '92 Lexus SC400. 210K miles. I have a code 52 (knock sensor), but I've already replaced it with a brand new one. The code cleared after I pulled the EFI fuse out. But then I got a code 71, EGR valve. Replaced that as well. COde 71 is gone, but now the code 52 is back. It's also running like crap. Sputtering in exhaust. And I hear air around the EGR valve, like a vacuum leak, but every thing is secured and tightened down. Now, what I have replaced is as follows (it's a long list, believe me)

1.) EGR Valve
2.) Both ignition coils
3.) All spark plugs
4.) Wires
5.) TPS
6.) IACV
7.) New gaskets for upper and lower intake manifold
8.) Cold Start Injector
9.) New gaskets for all components on upper intake manifold
10.) Cleaned ALL air grabbing areas and parts
11.) New Cold Air Intake Filter (Injen Intake for the last 3 years, no issues)
12.) All O2 sensors
13.) Pulled each injector, cleaned & replaced all O rings & reseated each one in the original socket
13.) Countless other things that I can't remember right now

ANY help is greatly appreciated as I'm completely and utterly lost... Thanks everyone...

 

I know the code has nothing to do with these but Fuel ECU and main ECU?

 

I did the Fuel ECU bypass, didn't change a thing. So I'm pretty sure it's not that. With the ECU, I'm hearing that they go out, which is fine, but because I'm still getting codes, doesn't that mean it's not shot yet? I'm just not sure which road to go down.

 

I deff would say its the ecu. Bad ecus can still throw codes. Try swapping with a friend's or go to a junkyard. If it works then get it rebuilt or keep new one.

 

^ before I read the other responses my first thought was a bad ECU. There's a few threads on here about the resistors or capacitors going bad on older ECU's and the car acting up - needing to be replaced with a new ECU. Do a search and you should find the threads.

 

You say that you hear something like a vacuum leak by your EGR valve? Check your EGR modulator; the diaphragm inside is notorious for cracking. Just take the lower hose off that connects it to the EGR valve and apply vacuum to it. If it holds, it's good. If not, replace it. They are $82 from Lexus of Atlanta. I replaced all the same things as you on my 90 LS and nothing stopped the bucking but that, and the engine temp sensor on the intake manifold. It's about $9. My car has much more power, better gas mileage, rich exhaust smell is gone, and most importantly the bucking is gone. The modulator was what finally cured it for mine.

 

[QUOTE=Lextacy09;8046604]Hey everyone... This is my third post so far about my issue. Everyone has been great with helping me and I really appreciate all of your words, advice, and guidance.

Here is where I am. I have replaced just about everything you can think of, and having a major issue with how I'm running. '92 Lexus SC400. 210K miles. I have a code 52 (knock sensor), but I've already replaced it with a brand new one. The code cleared after I pulled the EFI fuse out. But then I got a code 71, EGR valve. Replaced that as well. COde 71 is gone, but now the code 52 is back. It's also running like crap. Sputtering in exhaust. And I hear air around the EGR valve, like a vacuum leak, but every thing is secured and tightened down. Now, what I have replaced is as follows (it's a long list, believe me)

1.) EGR Valve
2.) Both ignition coils
3.) All spark plugs
4.) Wires
5.) TPS
6.) IACV
7.) New gaskets for upper and lower intake manifold
8.) Cold Start Injector
9.) New gaskets for all components on upper intake manifold
10.) Cleaned ALL air grabbing areas and parts
11.) New Cold Air Intake Filter (Injen Intake for the last 3 years, no issues)
12.) All O2 sensors
13.) Pulled each injector, cleaned & replaced all O rings & reseated each one in the original socket
13.) Countless other things that I can't remember right now

ANY help is greatly appreciated as I'm completely and utterly lost...

You say that you hear something like a vacuum leak by your EGR valve? Check your EGR modulator; the diaphragm inside is notorious for cracking. Just take the lower hose off that connects it to the EGR valve and apply vacuum to it. If it holds, it's good. If not, replace it. They are $82 from Lexus of Atlanta. I replaced all the same things as you on my 90 LS and nothing stopped the bucking but that, and the engine temp sensor on the intake manifold. It's about $9. My car has much more power, better gas mileage, rich exhaust smell is gone, and most importantly the bucking is gone. The modulator was what finally cured it for mine.

 

Check continuity from the ecu plug to the knock sensor to make sure there is no short within the wires.

 

If all this other stuff doesn't work and it is idling poorly, check each injector while it is running by pulling the injector wire off of one injector at a time. When you pull a wire and it idles worse, put that wire back on and move to the next injector. If you come across an injector that makes no difference when it is connected or not, that injector may be bad. I've also seen this happen when the timing belt gets changed and was installed improperly. Meaning it may be off a tooth or so on the cams causing the timing to be off.

Good luck with it. I'm sure between everyone on this forum you will get her running properly soon.

 

also check the pcv hoses and valve cover gaskets for leaks, this is all metered air.
Egr modulator is a good one too didn't think about that.