Originally Posted by aplagens05
Plenum bolts: 2 are broken (not by me) need to pull them out and get replacements. TB bolt for the bracket that attaches to the plenum well, one is stripped and again, needing replacement. Could these issues be causing the high RPM, or could it be the IACV? Its old, and I cleaned some oil residue off it when cleaning everything else. Also, is there a place to purchase the bolts, or just go to a hardware store and match them as best as possible?
To begin with, you need to replace the broken plenum bolts; by being broken, there could be a major vacuum leak possibly causing your problems.
If the same problems persist, then one of the first things to do is perform an ECU code readout with a portable scan tool to see if any fault codes are set. The tool can be purchased at most auto parts stores. Some of the conditions you're describing can be caused by a marginal crankshaft position sensor or a camshaft position sensor. If you're buying one or both of them, buy only OEM units from a new car dealer. Don't buy aftermarket types; they've been known to fail in a short time; some are even DOA.
At this point you'll have to determine if there's an ignition or fuel delivery problem:
* How long have you had the old spark plugs? If they are very old, then it's time for a set of new ones.
* Testing fuel delivery:
Tee-in a temporary fuel pressure gauge at the input to the fuel tube. The readings at idle should be as follows:
- with vacuum hose connected to the fuel pressure regulator: 34 psi
- with vacuum hose disconnected from the fuel pressure regulator: 43 psi
* There may be a major intake system vacuum leak:
To check the intake system for a vacuum leak, use a vacuum gauge for good accuracy; most auto parts stores sell vacuum gauges. attach the vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
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The vacuum gauge makes for a very good diagnostic tool. Here are some vacuum gauge readings and their indications:
Low & steady: Late ign timing/valve timing, low compression
Very low: Vacuum leak
High & steady: Early ignition timing
Gradual drop in reading from idle to higher RPMs: Excessive back pressure in exhaust system
Intermittent fluctuation at idle: Ignition miss, sticking valve
Needle fluctuates as engine speed increases: Ignition miss, blown head gasket, leaking valve or weak valve spring