brad11140

iTrader: (3)

Have a 93 sc400. Just got done replacing wires, rotors and plugs. At slower speeds the car kind of hesitates. I am keeping the gas pedel in one place and the car like eventually finds where it wants to be and accelerates. When I get on it hard it does fine. Transmission does not feel like it's slipping. Starts fine. Idles fine. Hopefully someone has seen this. I found another posting where the guy figured out it was an ignition coil. So I went and bought one. Swapped out drivers side. Still have problem. Swapped out passenger side. Still have problem.

There are the usual suspects. I suppose tps could be bad. Could a plugged catalytic converter cause this. Bad o2 sensor. I have no check engine lights on.

Help please.

brad11140

iTrader: (3)

Ooh yeah. The injectors were pulled and sent off for cleaning and flow testing. All new o-rings and such.

SCick300

Does it usually happen right after your transmission changes gears?

brad11140

iTrader: (3)

No, I would say it is at lower rpm's. The transmissions sounds and feels like it is changing gears at the appropriate times.

1JZPWRD

iTrader: (59)

Did it do this before you did these listed above, or you did these to try and fix the problem? Is it when the car is cold or hot, or anytime?

brad11140

iTrader: (3)

kind of hard to say. I have not had the car for very long and my first item of business was to change all of these things because the maintenance intervals were unknown. I seem to recall it hesitating when I was driving it home.

I have some interesting developments. When I came to work tonight I unplugged the battery to reset the ECU. When I started up it was running pretty bad. Idle was rough, than it smoothed out. Could have been an ECU issue. Has not did it again. I stopped for some food and before I left I unplugged the EGR connector. The rest of my drive was noticeably smoother, although the hesitation was still there, just not as pronounced. So I tried another experiment. I unplugged the MAF. Of course I get the check engine light, but the thing is running smooth as silk now. I plugged it back in and it seems to be gone. I have it sitting in the maintenance shop at work cooling off. I want to see if it repeats.

I am still going to change the fuel filterer because I have no idea of the last change.

DWPsc3

iTrader: (10)

Mayb you can double check all your wires make sure theres no dirt in the connectors or anything. I had a little dust inside one of my connectors last time and it made my car feel like it was about to stall out as i was driving

brad11140

iTrader: (3)

yeah I have been through the wires. Its just a weird problem. The car does not feel like its going to die. You hit the gas and it does not go anywhere, than it speeds up, than slows down and speeds up again. Above 2500 RPM it is sweet. I pulled the MAF off and cleaned it out with compressed air so I am going to see if that makes a difference. Fuel filter looks super simple to change so I will do that tomorrow night.

hovsc400

i had the same issue i got a 95 400 did all the things you did wit the wire, plugs, driver side coil and even threw in a timing belt job...after all that still had that hesitation at lower rpms.....and i just fixed it after all that and it was my spark plugs them selves i had normal plugs in it....swapped it out for the platinum as car requires platinum plugs properly gapped to .44 factory specs and magic all the power is back and no hesitation....so if havent used them get some plats plugs ngk, denso, bosch whatever you like and gap them right and you should be set

brad11140

iTrader: (3)

Put in NGK Iridiums. They come pre-gapped. I am trying not to have eureka syndrome but I think I nailed it down. When I leave the MAF unplugged the car has incredible power and absolutely ZERO hesitation. PLug it in and all the hesitation is back. So I think my MAF is not reading properly. I don't have a CEL so obviously it is still working. I need to look into this more because I am sure the MAF readings are part of an equation for fuel scheduling and if I unplug the MAF does it cancel out the equation and just fly by wire, meaning that the real problem if its not the MAF could be disabled ny unplugging the MAF. I need to go through the diagrams and see what else factors in.

brad11140

iTrader: (3)

I found some other posts on here referencing the engine coolant temp sensor.The ECT sensor is a major component in fuel scheduling. I did the resistance check on the MAF and it was good. The only thing you actually check in temp. On the wiring diagrams the ECT sensor ties in. So I think I might try changing this out before changing the MAF.

brad11140

iTrader: (3)

Decided to yank the IAC valve because I had seen a few postings as this having been the culprit of hesitation issues. Was pretty dirty. Cleaned it up and sprayed some penetrant in it. Resistance check was good. Hooked up battery to it and stroked the valve in and out. Worked fine. Could have been stuck. No way of really knowing I guess. At any rate, threw it back together and it is running great. No hesitation. Will see how the drive home is and will give an update later. I am still going to change the ECT sensor just to be sure. For $13 why not.

brad11140

iTrader: (3)

I think it might be fixed. Drive home this morning was noticeably better, but still slight slight hesitation at lower RPM's. I work graveyards, so after I got up I changed the ECT sensor and replaced the fuel filter. I would say it is 90% better. When engine is cold there is still slight hesitation that I am probably going to have to live with. Once it was warmed up there was zero hesitation. Ill road test for the next few days and let everyone know how it goes.

ZPEED

bypass the fuel ECU first..

brad11140

iTrader: (3)

Yeah Ill give that a try. Jumper Fp and +b in the diag connector correct?