Rj-lo

Before I start diving in to the repair shop Id like to get some ideas what could be happening..

This started a couple weeks ago but when i go to start the car either in the morning or after it has been sitting for awhile, it takes several cranks for it to finally catch. Once it finally does, the idle raises and lowers up to about 2000rpm and back down...almost like i have my foot on the gas pedal. Its not a battery issue, more thinking a fuel problem as my mpg have gone down significantly as well.

I have no idea when the MAF was cleaned, fuel pump was changed, or fuel filter was replaced as I bought this car used.

I did have the pcm tuned by ECS but that was about a month before all this started happening so I dont think that is the problem

Any help would be appreciated
Thanks

Rj-lo

Bill Curlee

Look at ALL the rubber vacuum lines and vacuum fitings attached to the intake manifold.

Especially the PCV hoses and tubing The PCV system lines, hoses and plastic tubing are top of the list on causing this issue. the rot and crack.

What year and type C5 do you have??

Makes a difference on the PVC system you have

Also make sure that ALL the intake ducting between the MAF and Throttle Body is intact and properly sealed. NO LEAKS.

You are most likely getting increased unmetered air in the engine which causes what you are expierencing.

Bill

Rj-lo

Ok thanks Ill check that out.
It only does it really on first start up in the mornings and very rarely once during the day.

Ive got a 98

Bill Curlee

Your PCV system routes around the BACK of the intake manifold. It has a Y assembly with plastic lines. They have been known to split and leak air:

Rj-lo

The problem went away briefly but now is back... and actually seems like its getting worse.
I used to be ok once the car got going, but now its shifting up and down while driving, rpms jump and lower at stop lights..sometimes even stalling, which takes awhile to get back started (no good at a drive thru!)

No, I never looked at the vacuum lines but I need to start checking everything. I had replaced spark plugs, cleaned MAF, replaced TPS, cleaned air fiter

All I can think of left is the vacuum leak, 02 sensors, clean the TB, IAC?
Other than that, the car goes off the cliff lol! kidding. (kinda :/)

Rj-lo

Shut up. It was the coolant sensor.
Car thought it was like -30 degrees outside and was trying to dump fuel like crazy.

Go figure... That's BS though. Glad it's fixed however

Stainsy

I am getting much the same thing on my car. I just bought it, have replaced the MAS, also new plugs, wires and had the air filters checked, replaced the fuel filter. My car has also been giving me codes P1153, however since it has a stage two cam, and a stage two intake, I was told that the computer hasn't been changed, so I will get these codes. My start up doesn't take several cranks, but lots of times it revs like 2000rpm in idle, and won't slow down unless I sit long at a light. Has stalled several times, and very hard to start again, way to much fuel. Where is the sensor you replaced, and how do you check it?

Dcollins3208

Your issue is likely a tuning issue. I was having a hanging idle problem with my HCI car, took it to a tuner and he fixed her up. What is your coolant temp reading on the DIC? Either way, the coolant temp sensor is on the engine block drivers side just to the left of the exhaust manifold (header).

Rj-lo

Take a look at the gauge on your cluster, then the DIC. The sensor is drivers side just below the alternator

Stainsy

Thank you both, I will check it tomorrow.