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FIXITMAN, Master Technician
Category: Lexus
Satisfied Customers: 17340
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95 SC400, has a hesitation/miss roughly between 12-1800 rpm.

Customer Question

95 SC400, has a hesitation/miss roughly between 12-1800 rpm. Only at light throttle, under load and when warmed up. When engine is cold, or at medium to WOT there is no miss or hesitation. It idles very smoothly at about 650 when warmed up and in park. It also does not act up when in park/neutral.
Recently replaced...
Timing belt, idler pulleys and tensioner
Crank and cam seals
Water pump
Distributor caps, rotors, ignition coils, wires and plugs
No CEL or codes stored in the ECU.
Here's a kicker... The TPS was out of adjustment, yet the car idled and ran fine(minus the hesitation mentioned above). After setting it to spec, the idle was high but the problem went away for about a day, then idle slowly lowered to normal and the problem came back. I feel as the problem might be TPS related, maybe.
What are your thoughts?
Submitted: 1 year ago.
Category: Lexus
Expert:  FIXITMAN replied 1 year ago.

Hello, my name is Bobby. Thank you for the question. Most of the time this is either an air flow meter issue or more commonly the throttle position sensor. Most of the time it is the throttle sensor. If you have the right scan tool you can monitor this and other times you can do it with a digital multi meter. It can be many other things, but these are the most common. Please let me know if you need more help.

Customer: replied 1 year ago.
Yeah, that answer isn't a whole lot of help. Starting with the TPS, do you have information as to what the proper method of adjusting and testing it would be?
Expert:  FIXITMAN replied 1 year ago.

Here is the instructions to install it. The clearance should be .16" of an inch.

Customer: replied 1 year ago.
I replaced the TPS with an OEM part, used the instructions provided to adjust it and it made no difference. I also temporarily swapped the MAF with a friend's car(same part number) which doesn't have the same problems as mine and it, too, made no difference. The problem is still there with new TPS and a known good MAF. Since the problem is only there when the engine is warm, I am wondering if it's a case of open/closed loop and possibly a bad O2 sensor, since the ECU does not rely on the O2 sensors while cold (open loop). What are your thoughts? How can I check O2 sensors without a scan tool?
Expert:  FIXITMAN replied 1 year ago.

Does your scan tool read live engine data?