Correct RPM @ idle, but it's still shaky, why?

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Joined
Dec 16, 2014
Threads
9
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Location
Western hemisphere
Website
www.tofel.eu
Hi guys!

Some time ago I've noticed an unpleasent idle, but it's only now that I have some time to look into it. I have no clue how what the car does is properly called in English (and that's also why it's hard for me to just search for answers on the Internet as I don't know what exactly search for), but when idling it shakes unevenly. I can feel and hear that the RPMs are not constant, but go up and down a bit all the time. That unpleasent shake reminds of a very preliminary and lightweight engine stalling (but that never happens and never reaches a level when it could possibly happen). How do you call that? Rough idle? Hesitation?

The problem only happens when the engine is HOT and gearbox is in "P" or "N" position with A/C OFF (when it's ON and RMPs are a bit higher I can't feel that shaking anymore). When the car is stopped, gear is in "D" and brake pedal is pressed (= car is stopped) then I experience no shaking at all and the engine is idling perfectly, the RPMs feel contant and even.

With HOT engine the RPM count is around 650 on "P" and "N" and around 750 - 800 when on "D" or with A/C ON (here it sometimes reaches 900 - 950).

If I remember correctly the issue developed after replacing a cracked hose leading to 'gas filter' from the vacuum piping system (part no. 23265). The 'gas filter' was replaced together with the hose. After that idling speed dropped from around 800 RPMs on "P"/"N" to current (and according to FSM the correct) value of 650.

So... my question is where to look for sources of that problem? It seems that this shaking is connected to too low RPM speed on "P" and "N", but as its value is as stated in FSM that should not be the case, right? So maybe there is a problem in vacuum system? There is a leak or it's clogged somewhere? (Do I remember correctly that vacuum piping used in "P" and "N" is different from the one used when in "D"?)

Oh, I've got P0401 MIL as well and so far could not locate it's source. If that shaking is caused by insufficient flow in EGR system shouldn't it also be noticeable when gear is in "D"?

I'd greatly appreciate your help as I'm in Todos Santos (Baja California Sur) without any plans to come back to US and I can't find any mechanic here who'd be knowledgeable in the subject. I've got one guy though, who's willing to look into the problem, but as he has little experience with vacuum/EGR I'd like to be able to point him in correct direction.

Cheers,
Bartek

Ps.
If that's a generic problem, which has been discussed here a million times already please tell me what to look for - how's that idling problem called?
 
I have no CEL. I have replaced EVERYTHING that could cause a 'shakey' idle & it still does it so I gave up. I've checked/replaced:
all vacuum lines
plugs
wires
cap
rotor
timing
fuel filter
air filter
fuel filter pump sock
cleaned TB
many, many bottles of fuel treatment
many different fuel stations/octane levels
I believe they all have inconsistent idle & always will regardless.
 
I have the exact same problem but no egr code. I just ordered a set of plugs hopefully that will help the shake. will keep you posted if it changes anything.
 
I have no CEL. I have replaced EVERYTHING that could cause a 'shakey' idle & it still does it so I gave up. I've checked/replaced:
all vacuum lines
plugs
wires
cap
rotor
timing
fuel filter
air filter
fuel filter pump sock
cleaned TB
many, many bottles of fuel treatment
many different fuel stations/octane levels
I believe they all have inconsistent idle & always will regardless.

I have done everything on this list within the last 10k miles except
cleaned TB
check timing
but I remember when I got the truck it ran as smooth as silk then all of a sudden from one day to the next the inconsistent idle started, not enough for the tachometer to measure a dip in rpms BUT noticeable to me.
 
Oh, looks like another unsolveable mistery (just like THE *clunk* in driveline?) with which one has to learn to live with? ;)

Guys, do you both have the problem only when in "P" or "N", but not in "D"? Or are the circumstances a bit different than in my case?

@LDF2037 from your list I've only cleand throttle body (port R was awfully clogged), replaced spark plugs (both things to days ago) and replaced all old hoses (three weeks ago). I have a fairly new air filter (1.8k miles on it) and used Lucas Fuel Injector Cleaner some 1k miles ago.

I had an oll leak from the distributor since I bought the truck (a month ago) and dudes here, who were fixing it did not set proper timing afterwards (I'm not also sure whether it was correct before that, but surely wasn't as bad as now). They'll play with it tomorrow so if that will prove to have any effect I'll let you know.

But if that's just the way it is maybe the only "fix" is to turn the A/C when in "P" / "N" or just keep it on "D" and break together. At least that's what I'm doing now as this inconsistent idle isn't very conforming and makes me frustrated right away ;)
 
I have no CEL. I have replaced EVERYTHING that could cause a 'shakey' idle & it still does it so I gave up. I've checked/replaced:
all vacuum lines
plugs
wires
cap
rotor
timing
fuel filter
air filter
fuel filter pump sock
cleaned TB
many, many bottles of fuel treatment
many different fuel stations/octane levels
I believe they all have inconsistent idle & always will regardless.

How old are your O2 sensors?
 
I have no CEL. I have replaced EVERYTHING that could cause a 'shakey' idle & it still does it so I gave up. I've checked/replaced:
all vacuum lines
plugs
wires
cap
rotor
timing
fuel filter
air filter
fuel filter pump sock
cleaned TB
many, many bottles of fuel treatment
many different fuel stations/octane levels
I believe they all have inconsistent idle & always will regardless.

How many miles? Have you done a compression and or leakdown test? Could be bad valve seals/seats, or a cylinder low on compression...
 
Could be a clogged Cat.
 
I have the problems in all gears if left in that gear for a few moments.
How old are your O2 sensors?
Forgot to add that I also replaced the front O2 as well. Rear is fine. Both are functioning properly while being monitored via Ultragauge.
I'm not trying to hijack the OP's thread. I'm content w/living w/my situation so please let's focus on his problem. I was only showing what I've checked/replaced to try to help him. Thanks anyways!
How many miles? Have you done a compression and or leakdown test? Could be bad valve seals/seats, or a cylinder low on compression...
I have not but I do get some good valve rattle when it's warm outside w/the engine @ normal operating temps. I'm no longer worried as it runs great, no CEL, not consuming abnormal amount of oil/fuel, etc. Thanks!
 
LFD2037 :beer:!

Ah, don't know whether that can provide any clues (or make some problem sources less probable), but I've got quite good MPG. In US on highways it was as high as 19 and here it's around 17 and has never been lower than 15. But... I usually cruise @ 55 MPH and I'm not a fan of rapid acceleration (that's reserved for motorbikes ;)).

When it comes to oil consumtion, then when checking with dipstick there is no visible loss after circa 1.5k miles (does it mean valve seals are fine?).

So guys... are there any probable causes that are quite easy to check by a mech, who doesn't have very sofisticated equipment and is not LC-experienced? I'd assume that compression test is out of question here, don't know about leakdown (what is it? bad valve seals?), clogged catalyst or O2 sensors...
 
On a 1996 if you had a misfire it would be telling you with a check engine light and a code and tell you which cylinder(s).

I wonder if you knocked off a vacuum line changing the fuel filter. Lay under the truck and look up at the bottom of the intake with a bright flashlight. Maybe you can see a hose that got knocked off?

If you have a vacuum leak, it might be on one cylinder plenum, causing a lean condition. This will speed up the engine when it fires that cylinder. Under load (in drive), it won't fluctuate so quickly, and you may not feel it shake.
 
Noticed on my '93 I just picked up that it has a little rough inconsistent idle when I first crank it. After I get going for a bit it calms down and is steady. How do you determine if you have a misfire?

Saying that there is duct tape around a portion of its throttle body right now :hmm:
 
I have the problems in all gears if left in that gear for a few moments.
Forgot to add that I also replaced the front O2 as well. Rear is fine. Both are functioning properly while being monitored via Ultragauge.
I'm not trying to hijack the OP's thread. I'm content w/living w/my situation so please let's focus on his problem. I was only showing what I've checked/replaced to try to help him. Thanks anyways!

I have not but I do get some good valve rattle when it's warm outside w/the engine @ normal operating temps. I'm no longer worried as it runs great, no CEL, not consuming abnormal amount of oil/fuel, etc. Thanks!


I'm curious as to how your Ultragauge provides data on the O2 sensors? I didn't see anything along those lines when setting up the ultragauge on my '97 LC. Thanks.




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Mine had this issue and I had the injectors professionally cleaned (outside of the truck) and replaced all the o-rings and base gaskets and it got alot better.
 
My 93 does this after I changed fuel pump and fuel filter. After a full tune up. It still has the problem. It stalls sometimes too. I didn't mind it but now it won't accelerate when I press the gas pedal. :/
 
All my Toyotas do it. All 3 of them, especially in Drive.
Get in a new one and only way to tell it's running is to look at the Tach.
They have all had tune up and have 0 chk engine lights.
I think on the Cruiser it is likely a vacuum leak. There is about 10,000 places it could leak.
 
Ive done pretty much what everyone else has done, except the injectors.

I chaulked it up to the AC compressor. In the Lexus, the AC is almost always cycling, since I leave it in AUTO. When I turn off the AC manually, my idle is very smooth (seat of the pants), but with the AC on the idle gets noticeably slightly rumbly (enough to notice, but not enough to worry about yet).
 
Vacuum leaks are always a dandy to trace, easiest ones to loose track of are the few under the upper intake plenum,
Easy way to find a leak is to spray with brake cleaner around the intake until u notice the engine running better and that will locate the general area of the leak
I picked up a cyl 1 mis and did everything under the sun and stars tune up wise with OEM parts, cleaned egr, intake, sent injectors out to be cleaned, fuel filter u name it, not tryin to scare anyone but in my case it was some shotty head work the previous owner had done,
So I got to do it again, with all OEM parts from CDAN!
 
I'm curious as to how your Ultragauge provides data on the O2 sensors? I didn't see anything along those lines when setting up the ultragauge on my '97 LC. Thanks.




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It tells you when they're in open loop, closed loop, voltage of front, voltage of rear, etc.
 

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