The car starts fine, but after a few seconds, it starts to run a little rough. Runs fine at speed, no apparent miss or lack of power. But at idle such as sitting at a stop light, the engine runs a little rough.

No check engine light.

Here is what I have tried, per suggestions from other threads:

1. New plugs and coil packs. The coil packs were original so I decided to replace them.
2. Cleaned the MAF sensor with MAF cleaner
3. Loosened the throttle cable slightly. Seemed to be just a touch snug. Now it seems right and snaps shut like it should.
4. Used a propane torch to shoot propane around the intake system to look for a vacuum leak. No apparent leak.
5. Ran two tanks of fuel injector cleaner thru the system.

None of these things have made any difference. I am suspicious of the throttle position sensor. If I very slightly advance the throttle at the throttle body by hand - VERY slightly advance it - the engine seems to stumble. If I continue to advance the throttle it “gets past it” and revs fine. When it returns to idle, it runs rough. Not horrible, but definitely not correct.

Faulty injector??

Your thoughts?

Thank you!

 

dirty fuel filter, worn fuel pump (s), timing has slipped (what secondary tensioners?), dirty throttle plate.

Can you read the fuel trims?

 

+1 get LTFTs

 

Ok I believe I will need an OBD tool for that. There seem to be two kinds....one that just reads the code, and one that gives real time data.

Where is the OBD plug located?

What brand/model of reader do I need?

Thank you again!

Edited to add: the secondary tensioners are third generation. I don’t think it’s a timing issue but I suppose it’s possible. Runs perfect once the throttle is a few millimeters past the closed position. Throttle plate seems clean unless I don’t know what you meant.

 

Further research shows that I probably need to take it to a repair shop with a professional scanner rather than buy one. Besides finding the fuel trims, apparently you can turn off the injectors one by one until you determine which one is bad.

Is it really possible to control the injectors like that on these cars??

 

But it may well not be an inj.

I'd start with LTFTs. Cheap DIY.

 

$25-35 for a Bluetooth OBD scanner and $10 for the Torque app for your phone is all you need to see a huge amount of information about your engine. Less $ than a single visit to a shop and you will have it forever and for every car you own.
I think you have an air leak and did not find it. Set up Torque to read short and long term fuel trims for both banks, then use a can of carb cleaner or electronics cleaner with the red straw to locate a leak. Check the underside of the intake tube, both PVC lines, the bypass hoses from the supercharger, etc. As soon as you see the STFT change you have found your leak

 

All that sounds right. I ordered a wireless obd scanner and looked at apps that will give me the required information. An air leak is possible. I will do my darndest to find out, and will report back after I get the readings.

Where is the obd port in the car?

 

above the gas pedal toward the right side

 

I plugged in my new wireless reader and used the dash command app to get the following fuel trim readings. I sprayed starting fluid quite liberally around the intake system, the supercharger, etc. I did not notice any change in RPM’s or in the fuel trim readings.

Please let me know what these readings should tell me.

 

Those trims indicate a serious problem if you followed the advice in the huge number of threads (do people ever read????) about when to read them.

Hot engine. Parked.
At idle then rev to about 2500.

 

Please see the new readings below. I am sure I have a problem, but I want to understand the readings. I would like to know why there are four banks showing. I thought there were only 2? And why are the readings so different between banks 1&2, and 3&4? The first 4 lines are banks 1&2, bottom ones are 3&4. Except I didn’t think there were 4 banks...?

That being said, the first pic shows a hot engine after several minutes at idle. The second picture is a hot engine after several minutes at 2500 rpm. When the car returned to idle, it began stumbling and running erratically.

No codes are thrown. And yes, I did read other threads and tried to do it correctly the first time. I put the readings in a different order today though, because I’m not sure which banks I was looking at yesterday. Please see my new readings here.

The order of the readings in both pics is banks 1-2 (LT & ST), and banks 3-4 (ST & LT). Any advice will be appreciated. Thanks again.



Reading at idle.





Reading at 2500 rpm.

 

With such large text and much of it trimmed off plus the multiple readings I do not know what the app is trying to say. Find a better app?

 

I can try that, but the only thing trimmed off is the bank number. I can see which bank it is when I click on it, so that’s why I clarified which banks are being displayed. But the percentages themselves are not cut off, at least on my screen. I’m not sure what the three smaller numbers to the right of each entry mean. No other info is present.

If this clarification doesn’t help, do you have an app preference that is better? I’m all ears! Just want to understand what I’m seeing and how to fix it....

 

Some idle speculation as I try to understand this: the computer thinks more air is coming in than it is, so it is trying to compensate by adding more fuel in order to keep the ratio in line. Is that right?

Or does it think the exhaust air is too lean, so it’s trying to make it richer on the front end?

Or am I asking the same question, just in two different ways?? I guess I’m thinking I could have a MAF problem or an O2 sensor problem. No codes tho......hmm....

The more I read, the less I know!

 

Try using the app differently or rescale the screen to read what it is trying to say or use Torque or almost anything else. Now it's worse than useless for you don't know which numbers to believe and which to ignore.

It's the worst I've seen in the last 15 or so years!

 

I went ahead and downloaded a different app. This one showed only 2 banks. Here are the screenshots. The numbers are bad. Further advice is needed...




At idle





At 2500 rpm

 

After this test I unplugged the MAF sensor just for fun. It stumbled but then snapped out of it and idled perfectly. It threw a bunch of codes tho. I plugged it back in and it immediately began running rough. I cleared the codes and they did not reappear, but it continued to idle rough.

Does that help in any way? Thanks again...I’m learning.

 

That points to the MAF, or the wiring going into the connector, does it look damaged or stretched in any way? Can you find another MAF sensor to swap and test? How did you clean the original MAF? Last thing, carry out a hard reset by dropping the neg cable off the battery and grab a coffee, pop it back on and see how it behaves then.

 

The wiring looks very good, at least to my eyes. I have done a number of hard resets as this problem began developing, which didn’t help. I cleaned it with CRC brand MAF cleaner, which didn’t help either. The only thing that helped so far was unplugging it! I am going to try to find one if I can and swap it out. If that doesn’t work I will go back to the drawing board.