im having a problem just recently with my 88 NA, Starts up and idle's to 3k as it would normaly and it runs fine until it gets to the actual idle speed around 750 then the engine starts to shake and stutter like crazy and my rev guage bounces between 750 and i say around 600-575, it wont die out so i guess im lucky there, it drives fine as long as its going past 750 revs it works perfectly but when it gets down there it always does it, this started happening last week. my first thoughts is that there could be an airleak somewhere. any thoughts? suggestions? i was also thinking that could it be caused by having the belts loose? like around the air compressor persay? i checked the tension and my belts are a bit somewhat loose but i dont have the time to actualy tighten them between school and full time job. so if someone can please give me some recomendations on what i should have it checked out for thnx.

 

vacuum leak

 

A leak before the throttlebody does a good job of giving you a rough idle. It happens a lot at the plastic intake elbow. Jam it on and re-tighten the hose clamp. If not there, look for blown off hoses.

 

I know this is going to sound extremly noobish and probally make all yall laugh up the yinyang but i just want to see if im on right on this. the intake elbow is what that huge black air pipe leading from the air filter to the intake is connected to isnt it?

if it is then ive already done what you've suggested. is there a picture or diagram you can link me to of the intake? my book doesnt really give me that good of a display of it to see where all the vacume hoses are located at to check for air leaks or if i need to replace them.

 

check your battery voltage and alternator output sometimes that could cause poor idle after warm up if anything just adjust your idle screw to like 850 rpm at idle

 

1. vacuum leak
2. leading plugs, wires or coil
3. timing
4. idle mixture
5. tps 'dropout' and or tps adjustment
6. BAC valve operation
7. Double throttle diaphragm (if failed can also be the source of a vac leak)
8. EGR valve stuck open
9. Check primary injectors for operating sounds (clicking)
10. Primary injector failed, clogged (blocked, partially blocked), leaking (too much flow, too rich)

Check voltage coming from the O2 sensor at idle. It should be rich (greater than 0.45v, and probably in the 0.55 to .7 v range). If the problem is a too lean mixture at idle (which would be characteristic of a vacuum leak), the O2 sensor voltage will be low (lean). If it is high (rich), the problem likely is not a vacuum leak.