My car had this issue last summer as well even before the SC was installed so I know it doesn't have to do with that. It seemed to go away last fall for a bit and has been doing it ever since I took it back out this spring. The car has no codes appearing either so I don't know where to look. I am actually really surpised it doesn't throw a code as the car really shakes and burbles to fire up and idle. If the car is warm after a drive it starts up smooth as anything, only when it's sat for a bit the car chokes for a second then revs and finds it's idle. I've tried cleaning the MAS and that doesn't seem to have any effect. Any ideas?

glad you posted this. I have the same issue.

Have you started with the basics,like chg plugs and wires. And possibly the fuel filter?

On some cars I've found that the cold start and warmup mixture need to be enriched slightly using DAS, but thats usually the 4cylinder engine, I've never needed to do it to a V8.

2 possibilities I can think of is an air leak around the injector seals and fuel mixtures not adapting properly.

The air leak at the injector seals is easy, just spray some water around them with the engine idling and the idle should change, if the engine is cold then try spraying with some WD-40 or similar.

The mixtures not adaptinig can be caused when the "sensor rotor adaption" isn't performed/completed. Basicly it's the teaching in of the crank angle sensor. If this isn't done then the long term mixture adaptions aren't learnt.
When you start the car it uses the defualt fuel mixture and only adjusts to what it needs once the 02 sensors are warm enough but it won't remember it for the next cold start. If you have had the battery disconnected for some time then this can cause it.


If you can check the mixture adaptions with a scanner and they are 1.00 or 0% then that's probably the cause. Sorry, i'm not sure how to reteach it without DAS. I'm sure someone else here might know.

This is definitely all possible but it's something I'd chk last.


Nitro again I'd question whether you've done a tune up and like Ausmb mentioned the O2 sensors would be the other thing. I chgd all four of my O2 sensors shortly after I bought my car. My mech recommended it as they do go on these cars. I've never experienced any of the symptoms your'e having.

I find that it is usually a air temp sender ? out of rangre when cold , but once in a while it is the engine temp sender . Way ?? As they start to get up in age , they get out of tolerence at the upper end & lower end of their scale range. Something I always do . I get a good accurate thermometer. . Leave the engine hood over night with the thermometer setting by the windshield. hook up your scanner tools. Turn on the ignition key , (BUT DON"T START THE mtr) All 3 temps should be with in , lets say 5 or 6 degrees of each other. This is a simple easy test , and may lead you a simple fix.

For air Vaccum leak detection , I use a spray can of Carb cleaner. Spray it around the injectors , gasket , seals , flanges / mating surfaces. Hose connection. If there is a vaccum leak it will find it. The motor will quit , stall. Stop running at the moment it sucks that stuff in through the effected area.

Have you ever had the ECU reflashed by an After market Tuner ?
Nice to see ProjectC55 back ___PTE___

Wow, didn't expect such complete answers. Thanks guys.

As far as everything goes...

1. plugs are wires are a little over a year old.
2. ECU is stock
3. 02 sensors have never been changed 69K on the car
4. Fuel filter is about 6 months old

I will check the temp sensors as mentioned PTE. Could one use the HVAC unit to read the sesors or do I need to plug in my cheapo depo scanner(which may not have temp readings)? I am also going to check some of my seals, is it ok to use MAS cleaner, or should I grab the ole' carb cleaner??

Also, without just buying and changing them, how does one if at all possible check the 02 sensors?

AusMBtech: very interesting about the startup A/F settings, beyond me so I will ask my tech up here.

Lastly, and most important, am I doing any damage to my motor with this happening?

Thanks a million guys!

I doubt it's doing any damage to your engine, but it's best to find out whats causing it anyway.

The o2 sensors will usually trip a fault code if they are againg but you can still check them. Witht the engine hot, use your scanner to check the voltages of the 02 sensors while holding approx 2000rpm for more than 30seconds. If the voltages fluctuate approx 400-500mV then they are still working.
They as they age they respond much slower to mixture changes and need hotter exhaust temps to work. Most common time to fault is in traffic because of extended idling causing low exhuast temps and the heater in the sensor isn't strong enough to keep it working.

I finished re-designing my intake yesterday and replaced my filter and MAF sensor at the same time. Car runs much better, smoother, and noticably crisp. While doing this I sprayed some MAF cleaner around the injector seals to see if that was the culprit. No luck. Car is running great except this morning I had the same rumble and shake down while the car was starting up.

I am going to see if my tech can read/scan and check the figures for my 02 sensors next. I am going to try the engine temp test tonight. My question is what I should use to find out my engine temp. I was wondering if it would be possible to use the climate control computer for reading the temps as it is #06 on the menu I believe.

Strange.

Just replaced my front to 02 sensors (the expensive ones) and started having this problem. I thought maybe it was just the computer adjusting or the car adjusting from running too rich for a month while I found 02 sensors.

Next up is a spark plug change.

try spraying carb cleaner around the shaft of the egr valve, see if that does anything for u