low rough idle on cold starts

K

Kkxrw

Joined
Oct 9, 2021
Messages
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Usa
Hi I have a problem that I have been struggling with on my 1994 FZJ80. I have searched this forum and read as much information as I could find but I have not found a solution.

Problem:
  • On a cold start the truck starts immediately
  • RPMs go to 1,100-1,200 and then 1-2 seconds later RPM's fall to 700-600
  • It idles very rough until it reaches normal operating temperature. The needle wanders a little
  • I can hear an occasional misfire
  • If I try to drive it before it is fully warm the truck hesitates and wants to stall out. It shakes
  • After it is warm it runs fine
The check engine light is NOT on but when I used a paper clip in the diagnostic box I get codes:
  • 12
  • 41
I have done the following to try to fix the problem but so for no luck. Any suggestions are very much appreciated.
  • Replaced the IAC - with a new Toyota Idle air control valve
  • Replaced the TPS - with a new Toyota Throttle position sensor
  • Replaced All vacuum lines
  • Replaced the charcoal canister
  • Replaced plugs with new Toyota OEM
  • Replaced cap and rotor with new Toyota OEM
  • Replaced wires with new Toyota OEM
  • Replaced the air filter
  • Replaced the gas filter near the throttle body with a new Toyota OEM
  • Replaced the thermostat with a new Toyota OEM
  • Cleaned the EGR valve with Sea Foam
  • Cleaned the throttle body with Sea Foam
  • Checked the wires at the distributor, IAC and TPS and they look fine (no broken wires or cuts in the plastic - they look solid)
  • Checked the wires at the computer (took out the glove box) and they look fine
  • Checked the mass air flow and it looks really clean
  • Checked for vacuum leaks with a cigar and vacuum tester and can not find any
I have pulled the EFI relay to reset the computer and drove the truck for a while but no change in behavior. I am going to check the temperature sensor (2 wire one) but other then that I am at a loss.

Any advise is greatly appreciated.

Thanks
 
ajax1

ajax1

Joined
Feb 7, 2009
Messages
2,639
Engine coolant temp sensor and or o2 sensors if you change these do both do both.
These years do not have a maf sensor it has a vaf sensor nothing to clean do not mess with the screws on top.
 
K

Kkxrw

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Messages
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Location
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Thanks. I am going to change the 2 wire temperature sensor. Are you sayi g if it change the 02 sensors do both? I am running out of things to check
 
b56tc

b56tc

Joined
Oct 20, 2005
Messages
223
Brother I am about as far from an expert on any of this as you can get but had similar, found a crack in the air intake hose, replaced OEM and fixed.

Amazing how brittle that rubber density gets when compared to a nice supple new one
 
K

Kkxrw

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Messages
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Location
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Brother I am about as far from an expert on any of this as you can get but had similar, found a crack in the air intake hose, replaced OEM and fixed.

Amazing how brittle that rubber density gets when compared to a nice supple new one
Thanks man but my hose is in really good shape
 
Ozark80

Ozark80

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Aug 20, 2021
Messages
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Northwest Arkansas
Have you done a compression and/or leakdown test?

I hate to be that guy, but AFAIK, occasionally a slowly failing HG can cause similar symptoms to what you're describing: rough idle and stalling on start-up.

Other than that, the only thing that comes to mind is overhauling any EGR components you haven't yet (VSV etc.), and cleaning any EGR ports you haven't gotten to yet, like in the upper intake etc.
 
K

Kkxrw

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I have not done a compression test

I cleaned the egr and replaced all hoses

I will look into the vsv next

thank you for the ideas!
 
K

Kkxrw

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Messages
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Today i changed the ecu water temperature sensor and no change. The truck still runs rough until it is fully warm. The engine pulsates. Any other ideas?
 
ppc

ppc

M Go Blue
Joined
Aug 18, 2003
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@Kkxrw, Which sensor did you replace.? There are two. One is associated with the dash panel gauge the other supplies temp to the ECU and would be the one you should have replaced.
 
K

Kkxrw

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The 2 wire temp sensor for the ecu was changed. After replacing it there was not change in performance. The truck still pulsates and idles rough until it is fully warm
 
K

Kkxrw

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Messages
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I checked for vacuum leaks again with propane and then again with intake cleaner.

I the used a vacuum gauge and it is steady at 21.

Somthing is not working properly until the truck is fully warm
 
Ozark80

Ozark80

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Messages
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Northwest Arkansas
Mine kinda idles rough and pulses a bit when it’s cold also. I think it’s a common thing with old Toyotas.

Do a compression/leak down, and maybe check your valve clearances also.
 
Kaosu

Kaosu

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Nov 28, 2021
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South Australia
Mine is doing the exact same and I'm going to get it tested (Compression and Leakdown) tomorrow so if I find anything I'll post it here.
 
K

Kkxrw

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Messages
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Mine kinda idles rough and pulses a bit when it’s cold also. I think it’s a common thing with old Toyotas.

Do a compression/leak down, and maybe check your valve clearances also.
Right. My pulses then When i drive it when its cold it hesitates real bad. I have not done a compreaaion test yet as i dont have a gauge. I did a vacuum test and once warm the needle is steady.

Ill look into valve clearance but would that be a problem all the time or just when cold? Thanks
 
K

Kkxrw

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Mine is doing the exact same and I'm going to get it tested (Compression and Leakdown) tomorrow so if I find anything I'll post it here.
Let me know what you find out. Thanks
 
Ozark80

Ozark80

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Right. My pulses then When i drive it when its cold it hesitates real bad. I have not done a compreaaion test yet as i dont have a gauge. I did a vacuum test and once warm the needle is steady.

Ill look into valve clearance but would that be a problem all the time or just when cold? Thanks
It’s possible. Wouldn’t hurt to check em anyway
 
R

robnicko

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Jan 12, 2016
Messages
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Australia
you mentioned an occasional misfire?

is this only when cold or when warm as well? when warmed up listen to the exhaust coming out the rear pipe at idle, is there a light popping sound? if so this could be an indication of a burnt valve or valve not seating properly (adjustment)
 
K

Kkxrw

Joined
Oct 9, 2021
Messages
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Location
Usa
you mentioned an occasional misfire?

is this only when cold or when warm as well? when warmed up listen to the exhaust coming out the rear pipe at idle, is there a light popping sound? if so this could be an indication of a burnt valve or valve not seating properly (adjustment)
Yes i hear the occasional mis fire when it is warm too. sometimes when i am driving i can feel it. It seems random

Do you think this is a different problem to the cold start running eough issue?
 
Irish Reiver

Irish Reiver

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@Kkxrw After you pull the fuses to reset the ECU, how long are you leaving it? The engine will idle real low until it relearns all the critical parameters. I can't remember exactly what Toyota states but I know it takes a few restarts and a few miles of driving. You may have fixed the issue but haven't given the ECU time to catch up.
 

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