xclo0siv

Hey I haven't posted much on this forum since I own an IS300 and am always on My.Is. Anyways, my dad's car is a 98 GS300. I've searched a LOT but could not find anyone with the same problems

The engine shakes RANDOMLY in sets.
-In Park, Neutral, Drive
-Whenever it shakes, the RPMs drop about 100 and climbs RIGHT back up
-Happens every 2-3 seconds when happening
-Most noticeable at slow speeds, especially at a stop
-Happens a few times a day
-Happens HOT or COLD
-Starts up GREAT
-Car does not smoke
-NO LIGHTS ARE ON AT ALL.

Some information that might be helpful:
-60k Maint was done 1 1/2 years ago.
-Car is currently at 75k
-I have seafoamed, cleaned the MAF, reset battery so far
-Car is leaking coolant


-I have eliminated a clogged up cat since this happens on COLD startups immediately
-Maybe coolant is leaking through the TB and possibly getting onto the spark plugs
-Bad Coil Packs
-Bad O2 Sensors
-Bad TPS Sensor
-Bad Spark Plugs
-Clogged Injectors

This weekend I plan on taking off the TB, cleaning it and checking the spark plug valley and spark plugs will change them accordingly.

RTIS250

iTrader: (9)

You say its leaking coolant. It woul definately be a good idea to find out where its leaking from, and where the coolant is going. Certainly if its leaking around the throttle body, then it can cause a misfire due to coolant on the coil packs or at the base of the sparkplugs. Sounds to me like a definate misfire. Look into the coolant leak. It would also be beneficial to hook up a scanner and see if you can see misfires on each individual cylinder while its happening. I doubt its an O2 sensor, TPS, or clogged injector.

xclo0siv

Update:

So this weekend I checked for a coolant leak but could not find anything. I am going to use the coolant sealer thing you put into the radiator to stop any leaks. Anyhow, I checked the two sparkplug wells that are easy to check and there was a bit of oil in each of them. The one near the back had lots of oil. So what does oil in the sparkplug well mean?

mitsuguy

iTrader: (2)

Good chance you have a spark plug wire or coil pack that is slowly dying...

I second what RTIS said, but will add that I've seen a TPS sensor go bad with that same symptom, however it was all the time, not intermittent...

I, too, would look at the misfire data... Pull the plugs and look for arcing along the white part (the insulator)... Anything that looks like a rusty line on one means the spark is arcing and full energy not getting into the cyinder... a dying coil pack will do the same, especially if theres a crack in its insulator that might be getting moisture into it....

if we are making a most likely culprit list:
spark plug wires, coil pack, spark plugs - in that order...
then, throttle position sensor, mass air flow sensor, oxygen sensor - in that order...

xclo0siv

Okay I will definitely check those out. I still could not find a coolant leak so maybe it could be a headgasket leak? The car has not been modified and is only at 70k miles right now so I'm not really sure. The heater does not work, coolant is disappearing and random hiccuping.

I will definitely change out the sparkplugs + wires first though. Is there something I can do to check headgasket?

Have a radiator shop check for coolant leaks or have a compression test?

Debonair

Most shops should be able to do a Cooling System Pressure test to see where the coolant is leaking. You can also look at the oil. If it is milky and looks like chocolate milk you most likely have a head gasket issue. Sometimes you can just look at the underside of the oil cap and find the milky build up that usually indicates coolant in the oil.

Most diagnostic techs will also have a Combustion Leak Tester that is placed on the radiator filler opening with the car running (if i remember correctly ). It has some special chemical in it that will change colors if there is a head gasket or block issue.

Here is a extreme example of the oil cap:

xclo0siv

Thanks debonair,

I will try to get a cooling system pressure test this weekend as well as swap out the plugs + wires. I hope this solves my problem :/.

Debonair

Just curious if you found anything on the car this weekend?

Caoboy

iTrader: (2)

All of these will throw a code though.

mitsuguy

iTrader: (2)

Usually, but not always... Depending on the type of failure, and especially if its not completely out of spec...