Full Throttle Car Not Accelerating?

[bssybeep]

I have an odd problem with my 1991 LS400 (101K miles). My car used to have terrific acceleration upon full throttle, the transmission would kick in and the car would take off like a rocket.

Just recently, I noticed when I depress the throttle fully, the car doesn't kick down and I get almost no acceleration or slow acceleration. The car kind of surges but goes nowhere. My engine rpms go up to 5000, but I'm hardly moving. The kicker is, the car runs fine on normal driving (street and mostly freeway) just seems to have a problem with full throttle kickdown.

It's weird, it appears maybe the tranny is acting up? But the car drives fine normally. Any help would be appreciated, Thanks in advance.

[91LS400vgb]

First things first - have you checked the transmission fluid level while the car is idling in PARK after the engine has reached normal operating temperature?

[bssybeep]

Thanks for the advice, I just checked it and it was down 1/8-1/4 of a qt. I just filled it and took it for a test drive. It appeared to kick down better upon initial full throttle, but once my engine reached ~5000 rpm the car felt like it was not pulling, ie. my engine was working, but the car was not moving faster.

[bssybeep]

I took the car out on the freeway. At 40-50mph, I punched it to merge into traffic, initially it appears to kick down, and the engine is revving up fine, but instead of a hard pull up to 80-100 mph, I get kind of a surging/stuttering effect with the car accelerating very slow and the engine revving up to 5000 rpm.

Under normal driving conditions, the car appears to be running and shifting fine.

[Threadcutter]

I took the car out on the freeway. At 40-50mph, I punched it to merge into traffic, initially it appears to kick down, and the engine is revving up fine, but instead of a hard pull up to 80-100 mph, I get kind of a surging/stuttering effect with the car accelerating very slow and the engine revving up to 5000 rpm.

Under normal driving conditions, the car appears to be running and shifting fine.

Guys:

Fuel Filter?...................

[monarch]

when I depress the throttle fully, the car doesn't kick down and I get almost no acceleration or slow acceleration. The car kind of surges but goes nowhere. My engine rpms go up to 5000, but I'm hardly moving.

5000 rpm without any or much gain in acceleration is usually a symptom of transmission slippage which in turn is usually a symptom of excessive transmission clutch pack wear. On the other hand, these transmissions have internal electronic shift controls and sometimes a weak / failing shift control solenoid can cause wierd shifting behavior. Lastly, these transmission require Toyota Type T-IV fluid. If Dexron fluid is used it might cause excessive transmission slippage.

If it were my car I'd drop the transmission oil pan and inspect the magnets in the pan and mesh of the metal filter screen for signs of excessive clutch pack wear debris. If there was not excessive debris then I would breathe a sign of relief and look for an electronic cause for the wierd shifting behavior. Excessive debris = spoonful amounts of debris clinging to the magnets and bottom of the transmission pan and the filter screen.

[bssybeep]

Thanks for the reply. From what I remember I thought I had the transmission flushed by Made-in-Japan a few years back. I'll need to check with them tomorrow to see what type of fluid they used. If they used Dexron instead of T-IV fluid, they may have ruined my tranny. I don't put many miles on my car so I wouldn't expect tranny problems so soon.

when I depress the throttle fully, the car doesn't kick down and I get almost no acceleration or slow acceleration. The car kind of surges but goes nowhere. My engine rpms go up to 5000, but I'm hardly moving.

5000 rpm without any or much gain in acceleration is usually a symptom of transmission slippage which in turn is usually a symptom of excessive transmission clutch pack wear. On the other hand, these transmissions have internal electronic shift controls and sometimes a weak / failing shift control solenoid can cause wierd shifting behavior. Lastly, these transmission require Toyota Type T-IV fluid. If Dexron fluid is used it might cause excessive transmission slippage.

If it were my car I'd drop the transmission oil pan and inspect the magnets in the pan and mesh of the metal filter screen for signs of excessive clutch pack wear debris. If there was not excessive debris then I would breathe a sign of relief and look for an electronic cause for the wierd shifting behavior. Excessive debris = spoonful amounts of debris clinging to the magnets and bottom of the transmission pan and the filter screen.

[bssybeep]

I just checked and it cost 240 to completely flush the tranny and torque converter. It cost $4000!! to replace the tranny. Since I am short on cash, what risk do I run that it will die on me completely if I just do nothing? Since it works fine on normal driving I guess I can live without a kickdown for awhile until my monetary situation improves. But I don't want to risk that the tranny may die completely.

Thanks in advance

[SRK]

Dexron won't ruin the trans, it will just make it shift differently. Have the car diagnosed by someone familiar with them, like a dealer with a good rep. The shift solenoids do give trouble sometimes, and they are not that expensive.

Don't worry about it, and don't spend money flushing the hell out of it, that isn't the problem.

[bssybeep]

Thanks for the reply. That makes me feel better because like an idiot I had added 1/4 qt of Dexron and then found out I needed type 4!!. I'm not sure what I'm going to do about that as the dealer said any other tranny fluid besides the type 4 is grittier, while the type 4 is finer and lubricates better. Therefore, the tranny will wear out faster with the dexron in it.

Regarding the original shifting problem, I'm bringing the car into the dealer on Monday, I'm hoping its the shift control solenoid, which to be honest it sounds like it is.

[maniek_LS]

I have an odd problem with my 1991 LS400 (101K miles). My car used to have terrific acceleration upon full throttle, the transmission would kick in and the car would take off like a rocket.

...

Hi,

Yesterday I got my car from mechanic (replaced damaged piston - there were no compression and engine knocked) and I made test drive. I was thunderstruck that car still have poor acceleration. I back to mechanic and ask him WHY ?!.

He told - all in your engine is like new (timing belt, valves adjustment, new wires, sparks) the only one thing which can be responsible to poor acceleration is... mas air flow sensor can be dirty or damaged.

Few minutes ago I did test (in Poland is 1.00 am and snow on roads :-) ) Before I start engine I disconnected MAF plug (of course check engine and TRC lights started ON), BUT ! Car start like a rocked I I'm sure I got 60mph in 8-9 seconds ! It accelerates very fast from beginning.

Next week I'll meet my colleague and borrow MAF for few miles test. Now I'm 75% sure that logy start of my LS is because MAF is dead.

Do you (someone of LOC members) know how to check MAF ? I need electrical parameters which must be meet by good MAF.

Thank you

BTW. bssybeep - try to disconnect MAF and make test road

[skylolow]

Have them also check your caty. converter. A clogged catyalic converter will do exactly what you said its doing. I would think your check engine light would be on if that is problem. I had a car once that had a clogged caty. and same thing, you get above 4,000 or so RPM's and the car just won't accelerate much more.

[bssybeep]

Thought I'd let everybody know the resolution to my problem. Maniek was the closest. Turns out my underhood insulation was coming loose and everytime I hit full throttle, it blocked my air instake! I never thought to look there. Eyeballing it, it didn't appear it was sagging. But the service manager said that was common and in fact called it when I first dropped off my car at the dealer. Thanks for all the assistance!

[maniek_LS]

Thought I'd let everybody know the resolution to my problem. Maniek was the closest. Turns out my underhood insulation was coming loose and everytime I hit full throttle, it blocked my air instake! I never thought to look there. Eyeballing it, it didn't appear it was sagging. But the service manager said that was common and in fact called it when I first dropped off my car at the dealer. Thanks for all the assistance!

Can you make a photo of damaged part ? I'm not understand all from your description.

Thanks

[KY350]

maniek LS - lift up the bonnet and you will notice that on the underside of the bonnet there is some insullating material. This became lose at the front and flopped over the air intake, blocking / reducing the flow of air to the plenum, causing the above mentioned problems.