I have been trying to hunt down and idling issue I have been having and so I replaced my TPS to see what would happen and I noticed that my timing advanced a lot and I cannot adjust the distributer enough to compensate for the difference is it supposed to do this or what could be happening? Also car idle around 1100rpm in park and about 1k in drive. I noticed if I turn the tps counter clockwise it will retard the timing to about 5btdc. Could TPS be out of adjustment or bad?

thanks

 

I have a basic set of instructions on how to check/set it if you think that would be helpful.to send that to you.

 

This is the greatest way to precisely adjust your TPS with a multimeter and a computer power connector. An extremely small adjustment makes a big difference and this makes sure it is dead nuts on. Just scroll down a bit to the TPS adjustment section one of the best hacks I've seen. If you don't have cable you can find it online for a couple dollars.

https://www.clublexus.com/forums/performance-and-maintenance/551125-the-definitive-guide-to-fixing-sc400-hesitation-issues.html

 

Ok I got the TPS dialed in and the timing is on point at 10btdc. Car drives nice n smooth no hesitation.

The only issue I am now experiencing is when I start the car from it already being warmed up from an earlier drive it will turn over and start fine but the rpm will drop and then the system catches it and shoots the rpm back up to idle, it will do this on occasion when I am coming to a stop or turning into a parking space and it will also do it going from park to drive, any ideas on this one?

thanks

 

Mine used to do something sort of like that back when it had knock sensor problems. It would bog down when coming to a stop, more so when running A/C. Often, that would be what triggered the knock sensor CEL and limp mode.

It turned out to be ECU damage. Separating the cause and effect with my symptoms would be tough, though.

Doing it while turning at slow speeds might indicate a power steering issue? I don't know if low fluid in the reservoir would cause that, but it's an easy thing to check.

 

Well I hope its not the ECU I did replace the capacitors this year along with the following,
Cap & Rotor
Plugs & Wires
tried a different AFM
tried a different IACV
fuel filter about 1yr ago
Air filter
Cleaned throttle body and IACV
throttle body gasket
IACV gasket
EGR Delete

It really seems like a vacuum leak however I cannot find it are there any common places for vacuum leaks. If I remove the vacuum hose from the back of intake manifold the car replicates same symptoms without changing RPM so leads me to think there is a vacuum leak somewhere, RPM is stuck at 1k in Drive it will not change unless I'm in Park or Neutral. Also I have noticed a slight hesitation when leaving from a stop, if I rev the engine in park the RPM will drop low as if it may stall but then bounce back up. The symptoms all seem to be common around a vacuum leak. Its driving me crazy.

thanks for the responses.

 

In that case, I'd rule the ECU out as a prime suspect. (Unless you had board damage from leaky caps.) Vacuum leaks definitely sounds plausible. If your vacuum hoses feel at all hard, they're probably cracking around the barbs and are worth replacing for about a buck a foot. If it's not the hoses, it could be the TB gasket, the silly non-functional o-rings on the IAC, manifold gaskets, etc.

Google ways of testing for vacuum leaks and choose the one you're most comfortable with.

 

I did replace TB gasket and IACV gasket however I will try some vacuum testing methods to see what I come up with, I will keep yall posted.

thanks

 

Have you looked at the vacuum receiver under the intake manifold that is like impossible to get to? I moved mine just because of the access. Could be a source of a leak, if your acis doesnt kick in at 4000 it might be an indicator.

 

You're thinking 2JZ, I take it? I was thinking 1UZ... Funny how our assumptions default to our main point of familiarity. Looking back, I don't see it specified one way or the other. The EGR vacuum mess on the 2JZ is straight up ridiculous. I had one of those hoses hanging loose when I got my '95 SC300. It's a knuckle and wrist breaker to reach down there and reconnect without removing the manifold, but doing that is quite difficult with the EGR in the way. Lose-lose. (With the EGR out of the way, most of the vacuum hoses can go bye-bye and the manifold is super easy to deal with.)

I see that in your list, sorry.

 

Sorry I did not clarify but it is sc300/2jz

I tried to do a leak down test by hitting some areas of the engine with carb cleaner to see if there was any change in idle but no luck, I will give it a try again later once I get home.

 

some additional details if I barely and I mean barely touch throttle it will hesitate and I even got it to stall by resting it in this position an engine light did come on before it stalled but I guess ECU did not save it because I tried to pull codes and there was none, does this set off any red flags of what it could be.