rct20

I need some help on diagnosing what may be causing this problem.

When I press the accelerator, sometimes I get no juice whatsoever. I don't mean the engine revs but doesn't catch and go like a transmission issue, I mean I can floor it and I get nothing but idle level rpms. Usually happens after a stop at a light, but also can occur while moving.

When it first started happening I took it in, and the mechanic wasn't able to replicate the occurence and thought it was all good. Also, he did a scan and said found nothing apparently wrong and was telling me to just come and pick it up. I said something's wrong, figure it out!

Then, he did another test drive and at one point the engine just stalled out and died in the middle of the drive. He recommended a complete tune-up and said the car had never had one based on what he described as OEM plugs ('91 with 83K miles).

Since then (2 weeks ago) it ran great, but just today started the same no rpms thing again. What could be causing this?

RTIS250

iTrader: (9)

What kind of car is it? You said it was a 91, is it an ES250 or LS... It sounds like the Mass Air Flow sensor to me. When its doing the no rpm thing, pop the hood, and give the MAF a light hit on top... sometimes the air flow door gets stuck. If this is the case, you will need a new one.

steviej

iTrader: (1)

RT, click on his profile button. 1991 LS 400.
also
what about the throttle position sensor or is the 91 LS a direct cable throttle assembly?

steviej

rct20

I took it into the dealership today and they say it needs a new fuel pump. Does that make sense. They said there is no evidience of anything else wrong, electronically, with sensors, etc. The fact the the engine light comes on as I start up and remains on for 10-15 minutes, the "radiator" light comes on and comes and goes (the thing that looks like the radiator, or the parthenon, I'm not sure what it's called), and sometimes the traction control light until warmed up...they say is all because the computer senses somethings wrong with the fuel pump and has no way of signalling that.

I'm no mechanic, but that all sounds like a bunch of BS to me. Are they playin' me, or does any of this make sense? This same dealership told me I needed a whole new/rebuilt tranny once and Aamco said I just was low on fluid, and everything's been fine since.

What do you guys think of the fuel pump diagnosis?

RTIS250

iTrader: (9)

Do you have any detail as far as their diagnostic procedure? If they put a fuel pressure gauge on the fuel rail, and while the car was experiencing the "no accel" problem he noted a significant drop in fuel pressure, then yes, it could very well be the fuel pump going bad. However, does the car act any differently? By that i mean, does it idle badly, almost die? Or does it just keep a steady idle, but wont accelerate?

rct20

No real clue on the procedure. It's a Lexus dealsrship in Manhattan, I figured they should know what they're doing (??) I can't even be sure if they were actually able to reproduce the situation. I didn't get to talk to the service people, the the office rep.

One time, prior to the tune-up though, I opened the hood as I was idling, just to look around (who knows what I thought Iwas gonna see, I'm sure your thinking) and the engine actually started revving up and down, sputtering, etc. all by itself, like it was possessed. I have never really noticed or experienced anything but steady quiet idling myself other than that one day. just the acceleration issue.

RTIS250

iTrader: (9)

If you've never experienced a rough or dying idle while its in the state of "no acceleration", i dont think it would be the fuel pump, however, its possible. Typically, with a loss of fuel pressure (assuming it wont let you rev because of lack of fuel), then you would have a lean condition, causing major misfires and a really rough running or dying engine (ive experienced just this one two early 90's LS's). In your case, i beleive its something such as the mass air flow sensor or throttle position sensor... I would request to hear the just why they think the fuel pump is bad, and not just a simple "the fuel pump is bad" answer. Good luck with it.

Lexs400

I am experiecing exactly the same scenerio with the LS and my dealer told me to have the TPS and mass airflow sensors replaced. However, I don't see the check engine or any other warning lights on. I was told that the tech, pulled the codes from the computer pointing to these two sensors. Question is: is it possible to have trouble codes present for these two components and not have the check engine or any other warning lights on in the dash ?

hyperopt

The MAF sensor in LS400 uses solid state vortex technique to measure mass air flow. There is no moving part or door to whack.