I have a 1988 pontiac firebird which has been running rough for some time, its been in the garage 4 tmes or more. its had compression test, lamber sensor,HT lead ,spark plug,inlet manifold gasket replaced,its cost me more than £800 altogether and its still not right.the car starts up no problem but after a couple of minutes the revs drop below 500 then back up to 1400 revs its up and down, if i dont give it any gas it will cut out.HELP.
Country: United KingdomMake: PontiacModel: FirebirdYear: 1988Engine: 5000cc TBI
I have'nt, a machanic who has his own garage and works on loads of yanks has done all the work on my car for the last 13 years.
Glad to be of help. Sounds like a bad IAC valve. See these links:
How to test
Are there any codes in computer? An IAC valve may not throw a code. You can try cleaning the valve first. I would also check or replace the coolant sensor if the engine has ever overheated.
The service engine light did come on twice this was weeks apart,it stayed on for about 15 minutes then went off but because i only use the car at weekends i disconnect the battery so the codes lost.I did change the thermostat about 2 years ago.I dont know if it helps you but but i have'nt done more than 1000 miles in the last 2 years.I took my car for a spin 2 weeks ago after the engine got warmed up, it ran great for some 20 miles but cut out on me when i was slowing down at a juction, scared the crap out of me so i have'nt been out in it since
First things you want to check for is cracked or leaking vacuum hoses and clean the IAC valve. The fluctuating idle indicates the problem lies with the IAC valve. If the problem is temperature related it's usually the coolant sensor. A problem with the EGR valve will only occur when at normal operating temperature and rpm is above 1500 rpm. It would be good to know what codes you have to know where to look. In any electrical problem you should first check the battery and clean battery terminal connections. A low or bad battery can cause many problems since it is the heart of your electrical system. Being that you don't drive much, it can lose it's charge. You should drive your car at least once a week.
Thanks very much for your help hopefully it will sort out the problem, will i need to use some sort of sealer when i replace the IAC valve or will it tighten down without any.many thanks wayne.
Use no sealer! Be careful not to overtighten. See: http://www.ehow.co.uk/how_7493011_remove-iac-valve.html
ASE Certified since 1972,Master Auto tech,Heavy Truck,4 years pontiac dealer Tech