I have an 86 2.8 and the rpm's have been jumping. I thought it was the engine missing. Replaced the TPS, Ignition coil, plugs and wires, cap and rotor, It first started at cruising speeds with light throttle. It now does it at all rpm's and at idle. I have even heard it backfire a couple times. Could this be an exhuast leak, just getting worse. The exhuast is getting louder and the there is a light popping that accompanies the rpm jumps. I don';t want to spend hundreds on a new exhaust if this isn't the main problem, and I never heard of exhaust leaks causing the rpm to jump. Anybody have a similar situation??

I also replaced the O2 sensor and fuel filter. There are no engine codes either (except code 32 if I drive on the freeway). . Compression is good on the rear 3 cylinders.

Have you checked you fuel pressure? You need a stable 40psi.
An exhaust leak can't cause problem but has to be fairly bad and in the right place. Leaks near the O2 can throw off the reading. Doubt it's that though.
Check the pressure and post back.

I'll stop by a shop today to check...thanks

Is your EGR valve working properly? Exhaust leaks at that can cause eratic idle. If you have a exhaust manifold leak, it usually just makes it idle very high like 1500 rpm, but I dont think it will make it jump up and down. Is your catalytic converter old...could be plugged but that usually causes loss of power at higher rpm. Are your plugs all in tight ?

I did the egr valve vacuum test and it was okay...although the solenoid does set off the code 32 on the freeway. I ordered the new style injectors but again I don't think an injector leak is the problem since I did the wire test on all cylinders and it was jumping the whole time. I will recheck the plugs just in case, thanks.

this also sounds like the first symptoms of a igntion module failing.
jumpy rpms, backfires & misses
also, the pick-up coil

where is the exhaust leak?

exhaust leak is at the muffler. I could try to replace the whole distributor i suppose. I think auto zone has one complete with module and pick-up for 120

Idle air control valve starting to die?

I replaced the idle air control valve last year. not sure that would cause this either. my car died over the weekend and it was the distributor cap and rotor. I have gone through 3 of those in 11 months! Just corrosion and build-up, no cracks. Car still bucking/missing

Are you also getting loss of power as well???
I had a miss..couldn't figure it out either.. changed ignition module..... changed plugs... still the same.. changed wires.... when I came to the coil wire.. found it had corrosion on the cap end.. after that was changed.. It idles like a dream now.....

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'86 Fastback SE 5 spd -'00 HD 1200XL Sportster -'99 Chevy K-1500 Z-71

well i replaced the plug wires and no change. it doesn't really have power loss, just misses (or whatever). it now seems to be steady while pedal is about half way down. however idle, light throttle, and full throttle all produce the missing effect. starting to believe it is an injector stuck open and dumping too much fuel in that cylinder

Ignition Module. My tach jumped all over before it died on the highway in rush hour(rush hour in Tulsa Oklahoma???? You bet).

well I just replaced all the injectors and still stumbles! GRRR! Now I have a 3000 RPM idle to go along with it! Must've cracked a vaccuum line while taking plenum off. Now to spend $118 on new vaccuum lines. And still no closer to an answer. Might have to go car shopping instead :-(